velocity and acceleration before contact in the tackle during rugby union matches

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Velocity and acceleration before contact in the tackleduring rugby union matchesSharief Hendricks a , David Karpul a , Fred Nicolls b & Michael Lambert aa UCT/MRC Research Unit for Exercise and Sports Medicine, Department of Human Biology ,Faculty of Health Sciences, University of Cape Town , Newlands , South Africab Department of Electrical Engineering , University of Cape Town , Newlands , South AfricaPublished online: 01 Aug 2012.

To cite this article: Sharief Hendricks , David Karpul , Fred Nicolls & Michael Lambert (2012) Velocity and accelerationbefore contact in the tackle during rugby union matches, Journal of Sports Sciences, 30:12, 1215-1224, DOI:10.1080/02640414.2012.707328

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Velocity and acceleration before contact in the tackle during rugbyunion matches

SHARIEF HENDRICKS1, DAVID KARPUL1, FRED NICOLLS2, & MICHAEL LAMBERT1

1UCT/MRC Research Unit for Exercise and Sports Medicine, Department of Human Biology, Faculty of Health Sciences,

University of Cape Town, Newlands, South Africa and 2Department of Electrical Engineering, University of Cape Town,

Newlands, South Africa

(Accepted 15 June 2012)

AbstractThe velocity and acceleration at which the ball-carrier or tackler enters the tackle may contribute to winning the contest andprevailing injury free. Velocity and acceleration have been quantified in controlled settings, whereas in match-play it has beensubjectively described. The purpose of this study was to determine the velocity and acceleration of the ball-carrier and tacklerbefore contact during match-play in three competitions (Super 14, Varsity Cup, and Under-19 Currie Cup). Using a two-dimensional scaled version of the field, the velocity and acceleration of the ball-carrier and tackler were measured at every 0.1s to contact for 0.5 s. For front-on tackles, a significant difference (P5 0.05) between the ball-carrier (4.6+ 1 m s1) andtackler (7.1+ 3.5 m s1) was found at the 0.5 s time to contact interval in the Varsity Cup. For side-on tackles, differencesbetween the two opposing players were found at 0.5 s (ball-carrier: 4.6+ 1.7 m s1; tackler: 3.1+ 1.2 m s1) and 0.4 s(ball-carrier: 6.3+ 2.3 m s1; tackler: 3.7+ 1.6 m s1) at Under-19 level. After 0.4 s, no significant differences (P4 0.05)were evident. Also, the ball-carriers velocity over the 0.5 s was relatively stable compared with that of the tackler. Resultssuggest that tacklers adjust their velocity to reach a suitable relative velocity before making contact with the ball-carrier.

Keywords: Tackle, rugby union, performance analysis, velocity, acceleration

Introduction

Rugby union is characterized by frequent bodily

collisions known as tackles. The nature of two or

more bodies colliding at such a high frequency

exposes players to muscle damage and a high risk of

injury (Hendricks & Lambert, 2010). It is therefore

not surprising that tackle-related injuries account for

up to 61% of all injuries during a rugby match

(Hendricks & Lambert, 2010). Players ability to win

the tackle contest has also been shown to have an

influence on the outcome of the match (Gabbett &

Kelly, 2007; Gabbett & Ryan, 2009; Wheeler,

Askew, & Sayers, 2010). These findings, coupled

to a need to further understand the complex

dynamics of the tackle contest (whether for injury

prevention, performance gains or research purposes),

has recently triggered an increase in the number of

studies on the tackle. These studies include identify-

ing risk factors for injury (Fuller et al., 2010;

Garraway et al., 1999; McIntosh, Savage, McCrory,

Frechede, & Wolfe, 2010; Quarrie & Hopkins, 2008;

Wilson, Quarrie, Milburn, & Chalmers, 1999),

analysing techniques and their association with

physiological and performance variables (Gabbett,

2008, 2009; Gabbett & Kelly, 2007; Gabbett &

Ryan, 2009), identifying factors that may predict

success in contact (Wheeler & Sayers, 2009; Wheeler

et al., 2010), and understanding the governing

dynamics of tackler/ball-carrier interactions (Brault,

Bideau, Craig, & Kulpa, 2010; Correia, Araujo,

Craig, & Passos, 2011; Meir, 2005; Mouchet, 2005;

Passos, Araujo, Davids, Gouveia, & Serpa, 2006;

Passos et al., 2008a; Passos et al., 2009; Passos,

Araujo, Davids, & Shuttleworth, 2008b; Sekiguchi

et al., 2011; Watson et al., 2011). To conduct these

studies, researchers commonly make use of video

analysis to analyse the tackle during match-play, or

study the tackle under controlled conditions.

Due to the complex and dynamic nature of the

tackle, multiple factors may contribute to a players

ability to win the tackle contest and prevail injury-

free. These factors are usually divided into intrinsic

Correspondence: S. Hendricks, UCT/MRC Research Unit for Exercise and Sports Medicine, University of Cape Town, PO Box 115, Newlands 7725, South

Africa. E-mail: [email protected]

Journal of Sports Sciences, August 2012; 30(12): 12151224

ISSN 0264-0414 print/ISSN 1466-447X online 2012 Taylor & Francishttp://dx.doi.org/10.1080/02640414.2012.707328

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and extrinsic factors. Intrinsic factors are inherent to

the player, and for the tackle constitute physical

characteristics, attitude, level of skill or technique,

movement efficacy, and experience (Hendricks,

Jordaan, & Lambert, 2012). In contrast, extrinsic

factors are beyond the control of the player, and

include coaching, training, behaviour, opponents

level of skill or technique, opponents movement

efficacy, and the environment (Hendricks et al.,

2012). More specifically, movement efficacy repre-

sents the velocity and acceleration of the ball-carrier

and tackler during the tackle. Research suggests that

these two physical components are important

determinants of the outcome of a tackle (Duthie,

Pyne, Marsh, & Hooper, 2006; Fuller et al., 2010;

Gabbett, 2008; McIntosh et al., 2010; Quarrie &

Hopkins, 2008; Wheeler et al., 2010). Velocity and

acceleration estimations at which players enter the

tackle have been reported for both match-play and

controlled conditions (Duthie et al., 2006; Fuller

et al., 2010; Gabbett, 2008, 2009; Gabbett & Kelly,

2007; Gabbett & Ryan, 2009; Garraway et al.,

1999; Grant et al., 2003; McIntosh et al., 2010;

Pain, Tsui, & Cove, 2008; Passos et al., 2008a;

Quarrie & Hopkins, 2008; Walsh, Young, Hill,

Kittredge, & Horn, 2007; Wheeler & Sayers, 2010;

Wheeler et al., 2010). However, during match-play

these estimations of velocity have been subjectively

described compared with controlled conditions in

which actual velocity and acceleration measure-

ments were recorded (Fuller et al., 2010; Gabbett,

2008; Garraway et al., 1999; McIntosh et al., 2010;

Quarrie & Hopkins, 2008). In controlled settings,

velocities range from 1.5 m s1 to 4.6 m s1 forthe tackler, and from 1.5 m s1 to 5.9 m s1 forthe ball-carrier (Gabbett, 2009; Gabbett & Kelly,

2007; Gabbett & Ryan, 2009; Pain et al., 2008;

Passos et al., 2008a; Wheeler & Sayers, 2010). The

range of these velocity measurements for both ball-

carrier and tackler can be explained by the different

study designs, aims, and competitive level of the

players. Studies in controlled settings are further

limited because the velocities of the ball-carrier and

tacklers are usually measured in isolation (Gabbett,

2009; Gabbett & Kelly, 2007; Gabbett & Ryan,

2009; Pain et al., 2008; Wheeler & Sayers, 2010).

Furthermore, to control the conditions of the

tackle, either one (Gabbett & Kelly, 2007; Pain

et al., 2008) or both players (Wheeler & Sayers,

2010) in the tackle were given instructions on their

movement, limiting the velocity measurement and

rendering the tackle unrealistic compared with

match-play. Further limitations of studies con-

ducted in controlled settings include no contact

between the two opposing players (Wheeler &

Sayers, 2010) and the use of a stationary tackle

bag as opposition (Pain et al., 2008). With the use

of video analysis, speed or velocity before the tackle

has also been subjectively described during match-

play.

These descriptive measurements have been

shown to be effective in characterizing different

velocities as risk factors for injury and prerequisites

for success in contact (Fuller et al., 2010; Garraway

et al., 1999; McIntosh et al., 2010; Quarrie &

Hopkins, 2008).

Video analysis in combination with computer-

generated algorithms is an accurate method to

calculate linear distance over time (Barris & Button,

2008; Edgecomb & Norton, 2006). This method

relies predominately on ground markings as refer-

ence points to reconstruct a two-dimensional scaled

version of a playing field (Brewin & Kerwin, 2003;

Edgecomb & Norton, 2006). A major advantage of

this approach is that it is independent of camera

angle to the plane of motion (Alcock, Hunter, &

Brown, 2009; Kwon & Casebolt, 2006). Therefore, it

is possible to reconstruct playing fields from televized

footage as knowledge of camera set-up is not

required (Alcock et al., 2009). This method has

been used in football (Carling, Bloomfield, Nelsen,

& Reilly, 2008; Mallo, Veiga, de Lopez, & Navarro,

2010), Australian rules football (McIntosh,

McCrory, & Comerford, 2000), rugby league

(McIntosh et al., 2000), and rugby union (Correia

et al., 2011). McIntosh and colleagues (2000) used

this method to compare concussive head impacts in

Australian rules football, rugby league, and rugby

union. One such comparison was players velocity

before the impact. Australian rules football players

averaged 7 m s1 (range 0.213.8 m s1) beforeimpact, whereas the average velocity measured for

rugby league was 6 m s1 (range 3.011.4 m s1)and for rugby union it was reported to be 5 m s1(range 3.57.7 m s1) (McIntosh et al., 2000).Although McIntosh and colleagues (2000) reported

velocity before contact, they did not differentiate

between the type of contact (i.e. tackle, ruck,

collision) or indicate the role of the players in the

contact (i.e. ball-carrier or tackler).

To develop effective training strategies (i.e. tech-

nical skills training, physical conditioning, training

drills, and equipment used) that will produce a

successful outcome and reduce the risk of injury for

both ball-carrier and tackler, a further understanding

of tackle dynamics during match-play is warranted.

Basic physical components of the tackle during

match-play, such as velocity and acceleration, are

yet to be quantified and reported. Therefore, the

purpose of this study was to determine the velocity

and acceleration of the ball-carrier and tackler before

contact for three different competitions using video

analysis in combination with computer-generated

algorithms.

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Methods

Nine rugby union matches from Super 14 2010

(three matches), an elite international competition

consisting of full-time professional rugby players

from provincial franchises in Australia, South Africa,

and New Zealand; Varsity Cup 2010 (two matches),

a highly competitive national university competition

consisting of semi-professional players; and Under-

19 Currie Cup 2010 (four matches), a competition

consisting of highly trained schoolboy players were

randomly selected and analysed for this study.

Televised recordings were used and self-recorded

video footage was used for Varsity Cup matches.

Ethics approval for this study was granted by

University of Cape Town Research Ethics Committee.

Front-on and side-on tackles during each match

were coded using Sportscode Elite (Version 6.5.1,

Sportstec, Australia). A tackle was identified when

ball-carrier was contacted (hit and/or held) by an

opponent (tackler) without reference to whether the

ball-carrier went to ground (Fuller et al., 2010;

Quarrie & Hopkins, 2008). Tackles were further

classified into front-on and side-on tackles. Front-on

tackles were coded when the anterior body parts of

the ball-carrier were contacted first by the tackler

(Quarrie & Hopkins, 2008), whereas side-on tackles

were identified when the lateral body parts (on either

side) of the ball-carrier were contacted first by the

tackler (Quarrie & Hopkins, 2008). The video

footage of the tackle event had to fulfil the following

visibility criteria: (1) a visual of four locations with

known distances represented by the lines on the field;

(2) a clear running path of the ball-carrier and

primary tackler pre-tackle (at least for 0.5 s); and (3)

the camera had to remain fixed over this period.

Tackle events that fulfilled these criteria (10 tackles

6 3 competitions 6 2 types of tackles 60 tackles)were subsequently imported into Dartfish Teampro

(Version 4.0.9.0, Dartfish, Switzerland). Apart from

identifying front-on and side-on tackles, tackles were

randomly selected irrespective of team, playing

position, field location, set piece/breakdown that

preceded the tackle, or any other tackle

characteristic.

Using Dartfish Analyser, a timer was set to zero at

the point of contact between the ball-carrier and

primary tackler. The ball-carrier and tackler were

then retracted for 0.5 s (25 frames) from the point of

contact. This period is considered the pre-tackle

phase (Fuller et al., 2010). Thereafter, the ball-carrier

and tackler were tracked back to the point of contact

for the 0.5 s. Ball-carriers were generally tracked from

mid-section (hip area) and tacklers on the upper

body. The rationale for this is that during most

tackles, tacklers enter the tackle with their upper body

as the first point of contact. A line was then drawn

with the software through the tracked path of both the

ball-carrier and tackler, and divided into 0.1 s

intervals (five 0.1 s intervals, six markings) (Figure

1). An image of the analysed tackle, with the marked

0.1 s intervals, was subsequently imported into

Matlab (Version 6.5, Mathworks, Inc., Natick, MA).

An algorithm to determine the planar location of a

single point determined by pixel coordinates within

an image was developed in Matlab. As mentioned

earlier, one of the inclusion criteria for analysis of the

tackle event was a visual of four locations with known

distances represented by the lines on the field. This

made it possible to enter four known x and y

coordinates on the field. The program then created a

two-dimensional (2D) axis (x; y) system in the plane

of the field shown in the imported image from

Dartfish. Once the four known coordinates were

entered, and the 2D-axis system created, it was

possible to obtain x; y coordinates of any point on the

field. To obtain the coordinates, the analyser had to

simply select any point on the field, and the

algorithm would calculate the coordinates despite

the projective distortion to the image created by the

camera. For every tackle event, a new image and a

new 2D-axis system was created, according to the

known distances. Before a tackle was analysed, and

to further validate the 2D-axis system, coordinates

produced by the 2D-axis system had to correspond

to the known distances of the playing field from the

imported image.

The centre of the field (on the half-way line at the

mid-point between the two touchlines) was chosen

as the point of origin on the field (x 0; y 0)(Figure 2). After validation, the coordinates of the

marked 0.1 s intervals were obtained for both the

ball-carrier and the tackler. The distance between

Figure 1. Graphic representation of time to contact measurement points.

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two coordinates (x and y) was calculated and divided

by 0.1 s to produce the average velocity over that

interval. This was repeated for the five 0.1 s intervals

up to the point of contact for both ball-carrier and

tackler. Average acceleration over the 0.5 s was

calculated by subtracting the final velocity by the

initial velocity, and dividing it by 0.4 (only four

intervals of acceleration over the 0.5 s).

Validation

To test the validity of our methods, velocity

measurements using the methods described above

were compared with criterion velocity measure-

ments. A contact zone was created and located at

three different points between the two 15 m lines:

one furthest away from the camera, one in the centre

on the field, and one closest to the camera. The

contact zone consisted of six cones placed 0.5 m

apart from each other. One Varsity cup backline

player was asked to carry the ball into contact and

execute a tackle in each contact zone three times,

respectively (nine ball-carries and nine tackles).

When performing a ball-carry or tackle, the player

was asked to execute with the same intensity as he

would during a competitive match. In addition, an

extra 2.5 m was included before the contact zone to

allow the player to gain speed and enter the contact

zone at a velocity similar to that he would attain

during match-play. Another Varsity Cup player

provided the opposition in each case. Each contact

was recorded using a digital camera (Sony HDV,

HVR-A1E, Japan) and imported into Dartfish

Teampro.

Measurement velocity was determined using the

methods described above. Criterion velocity was

determined using the known distances indicated by

the cones. In Dartfish Analyser, the known distances

of the cones were set as reference points and

recorded for the five 0.1 s intervals. As mentioned

previously, a further validation was also conducted

on each image by confirming that the coordinates

produced by the 2D-axis system corresponded to the

known distances of the playing field.

Statistical analysis

Validation. Correlation coefficients (r) were calcu-

lated to measure the relationship between the

criterion velocity and the measurement velocity.

Standard error of the estimate (SEE) was determined

to analyse the amount of error in the measurement

(Jennings, Cormack, Coutts, Boyd, & Aughey,

2010). The Bland-Altman test was used to measure

the mean difference and limits of agreement (LOA mean difference + 2 standard deviations) betweenthe criterion velocity and the measurement velocity

(Bland & Altman, 1986; Nevill, 1996; Nevill &

Atkinson, 1997).

Velocity. Analysis of variance was used to compare

the average velocity of the ball-carrier and tackler for

front-on and side-on tackles across competitions.

Analysis of variance was also used to compare the

velocity of the ball-carrier and tackler in different

competitions at each 0.1 s time to contact interval

during front-on and side-on tackles. A Tukey post-

hoc test was used to further analyse any differences

Figure 2. Graphic representation of a rigby field showing x and y coordinates determined from lines on the field. Note that this

representation only shows some of the coordinates on one side of the field.


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found. We use t-tests to compare the average

velocity, and each of the five 0.1 s intervals between

ball-carrier and tackler during front-on and side-on

tackles for all competitions and within each competi-

tion. All velocity data are reported as means +standard deviations (mean+ s).

Acceleration. Analysis of variance was used to compare

the mean acceleration of the ball-carrier and tackler

for front-on and side-on tackles in all three competi-

tions. We used t-tests to compare mean acceleration

between ball-carrier and tackler during front-on and

side-on tackles for all competitions and within each

competition. All acceleration data are reported as

means + standard deviations (mean+ s).

Results

Validation

Figure 3 shows acceptable reproducibility and

agreement between the criterion velocity and the

measurement velocity for both ball-carrier and

tackler. For the ball-carrier, higher correlation

coefficients and smaller standard errors of the

estimate were found closer to the point of contact.

Also, the mean differences between the criterion

velocity and the measurement velocity for the ball-

carrier over the 0.5 s pre-tackle period were below 0.5

m s1 (Figure 3). For the tackler, high correlationcoefficients and small standard errors of the estimate

are distributed over the 0.5 s pre-tackle period. The

mean difference between the criterion velocity and

the measurement velocity at 0.5 s to contact for the

tackler was 0.62 m s1, and decreased thereafter ateach time to contact interval (Figure 3).

Velocity before a front-on tackle

During the front-on tackle, the average velocity over

the 0.5 s period for the ball-carrier in each respective

competition was 4.8+ 2.9 m s1 (Super 14), 5.2+ 1m s1 (Varsity Cup), and 4.9+ 1.7 m s1 (Under19) (Table I). The corresponding average values for

the tackler were 5.0+ 1.8 m s1 (Super 14),6.4+ 2.6 m s1 (Varsity Cup), and 5.7+ 1.9 m s1 (Under 19) respectively. No significant differ-

ences were observed between the competitions for the

ball-carrier and tackler when comparing each 0.1 s

time interval (Figure 4).

No significant differences were found between the

average velocities of the ball-carrier and tackler

overall for all competitions and within each competi-

tion. However, a significant difference between the

ball-carrier and tackler was found at the 0.5 s time to

contact interval, overall for all competitions, and

specifically within the Varsity Cup (P5 0.05). At this

time to contact interval, the overall movement

velocity of the tackler was 6.6+ 3.1 m s1, whereasoverall movement velocity of the ball-carrier was

5.0+ 2.5 m s1. At the 0.5 s time to contact intervalin the Varsity Cup, tacklers were entering the pre-

contact phase at 7.1+ 3.5 m s1, compared with4.6+ 1.0 m s1 for the ball-carriers. For theremaining time to contact points, no significant

differences were found, for all competitions and

within each competition.

Velocity before a side-on tackle

During the side-on tackle, the average velocity over

the 0.5 s period for the ball-carrier in each respective

Figure 3. Relationship between criterion velocity and measure-

ment velocity at each 0.1 s interval for 0.5 s before contact. r correlation coefficient; SEE standard error of estimate.


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competition was 4.9+ 2.1 m s1 (Super 14),5.8+ 1.8 m s1 (Varsity Cup), and 4.7+ 1.3 m s1 (Under 19) (Table I). The corresponding average

values for the tackler were 5.4+ 2.2 m s1 (Super14), 5.5+ 2.1 m s1 (Varsity Cup), and 3.9+ 1.1 m s1 (Under 19) respectively. No significant differ-ence was found between the average velocities of

the three competitions for both ball-carrier and

tackler.

A significant difference was found between the

tacklers of the different competitions at the 0.5 s time

to contact interval (P5 0.05) (Figure 5). A Tukeypost-hoc test revealed that this significant difference

was between Varsity Cup and Under-19 (P5 0.05).No significant difference was found between the

average velocities of the ball-carrier and tackler

overall for all competitions and within each competi-

tion. Significant differences between the tackler and

ball-carrier were found at the 0.5 s and 0.4 s time to

contact intervals in the Under-19 competition

(P5 0.05).

Acceleration before a front-on and side-on tackle

No significant differences were found between the

mean accelerations of the three competitions for both

ball-carrier and tackler during front-on and side-on

tackles (Table II). No significant difference was

found between ball-carrier and tackler overall for all

competitions. However, a significant difference was

found between the mean acceleration of the ball-

carrier and tackler during a front-on tackle in the

Varsity Cup.

Discussion

This is the first study to objectively report the velocity

and acceleration of both ball-carrier and tackler

during rugby union match-play. Moreover, these

velocities and accelerations were revealed for front-

on and side-on tackles across three competitions.

When entering a front-on tackle, no significant

differences were found between the competitions

for both the ball-carrier and tackler when comparing

the average velocity, average acceleration, and the

velocity at each time to contact interval. This was

also evident during the side-on tackle (except for the

tackler at the 0.5 s to contact interval where a

difference was found between Varsity Cup and

Under-19). These findings suggest that the velocity

at which players enter the tackle may not be a good

indicator of playing standard. This explanation is

supported by the velocity measurements for the ball-

carrier and tackler in controlled conditions where

players of national and international standing do not

differ substantially from sub-elite, amateur or junior

levels (Gabbett, 2009; Gabbett & Kelly, 2007;

Gabbett & Ryan, 2009; Pain et al., 2008; Passos

et al., 2008a; Wheeler & Sayers, 2010). Alternatively,

the three competitions used in this study did not

differ enough to note any pre-tackle velocity dispa-

rities, since all three competitions consist of high-level

players, with considerable experience and quality

training habits. Further research, with perhaps a

greater disparity in playing standard (for example,

amateur vs. professional) and a larger sample size, is

needed to draw any definitive conclusions.

When comparing the velocities between ball-

carriers and tacklers before contact in front-on and

side-on tackles, significant differences were found at

Table I. Average velocity and velocity ranges for ball-carrier and

tackler before contact during front-on and side-on tackles at each

0.1 s time interval.

Time to contact (s)

Ball-carrier

velocity (m s1)Tackler velocity

(m s1)

Mean Range Mean Range

Front-on

0.5# S14 5.3 1.85.4 6.3 3.314.6

VC* 4.6 3.16.1 7.1 2.711.5

U19 5.1 2.09.3 6.5 3.310.8

0.4 S14 4.8 1.19.9 4.3 1.09.8

VC 4.7 2.87.3 7.3 1.415.2

U19 5.2 1.811.2 5.0 2.910.1

0.3 S14 5.0 1.513.2 4.5 0.77.5

VC 5.8 3.38.5 6.8 1.413.9

U19 4.6 1.88.0 6.3 2.710.2

0.2 S14 4.2 0.79.8 4.1 1.58.8

VC 5.4 3.47.8 6.4 1.714.3

U19 4.6 1.89.5 5.5 3.09.4

0.1 S14 4.8 0.712.6 5.6 1.711.2

VC 5.4 2.68.9 4.5 2.68.2

U19 4.8 1.411.8 5.4 1.08.8

Average over

0.5 s to contact

S14 4.8 1.212.2 5.0 1.67.9

VC 5.2 3.86.5 6.4 2.410.8

U19 4.9 2.97.9 5.7 3.58.9

Side-on

0.5 S14 5.2 1.713.9 6.2 2.114.7

VC 5.8 2.39.6 7.3** 3.415.1

U19* 4.6 2.97.6 3.1** 1.55.4

0.4 S14 4.9 1.911.0 5.1 1.212.2

VC 6.2 2.312.1 5.8 1.010.9

U19 6.3 1.49.0 3.7 1.46.0

0.3 S14 4.9 2.49.7 6.2 2.912.5

VC 6.0 2.39.0 4.7 0.79.1

U19 4.6 2.46.7 3.7 1.55.6

0.2 S14 4.6 1.011.0 4.4 1.610.8

VC 5.3 1.411.1 4.5 0.77.5

U19 4.4 1.810.4 4.7 2.38.1

0.1 S14 4.7 1.212.2 5.2 1.99.2

VC 5.5 1.513.2 5.2 2.79.0

U19 3.7 1.66.2 4.2 1.56.6

Average over

0.5 s to contact

S14 4.9 2.79.1 5.4 2.28.8

VC 5.8 2.69.2 5.5 3.19.6

U19 4.7 2.77.2 3.9 2.05.8

#Overall significant difference for all competitions (P 5 0.05).*Significant difference between ball-carrier and tackler within

competition (P 5 0.05).**Significant difference between competitions (P 5 0.05).


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the furthest points from contact: 0.4 and 0.5 s away

from contact. As contact approached, these differ-

ences between the ball-carrier and tackler were found

to be insignificant. Furthermore, for both front-on

and side tackles, the ball-carriers velocity along each

time to contact interval seemed relatively stable

compared with the variability in the tacklers time

to contact intervals. These results suggest that when

tacklers enter the pre-tackle phase at a velocity

considerably different to that of the ball-carrier

(whether higher or lower), a counterbalance reaction

is initiated.

Tacklers achieve this counterbalance during the

last moments in the pre-tackle phase by adjusting

their velocity accordingly. These findings support

research by Passos et al. (2008a) on the governing

dynamics between attacker (ball-carrier) and

Figure 4. Ball-carrier (positive) and tackler (negative) velocities

before contact during a front-on tackle in Super 14, Varsity Cup,

and Under-19 competition. Velocities measured at each 0.1 s

interval for 0.5 s. Data are means + standard deviations. *Ball-carrier (BC) significantliy different from tackler (T) at 0.5 s to

contact (P 5 0.05).

Figure 5. Ball-carrier (positive) and tackler (negative) velocities

before contact during a side-on tackle in Super 14, Varsity Cup,

and Under-19 competition. Velocities measured at each 0.1 s

interval for 0.5 s. Data are means + standard deviations. *Ball-carrier significantliy different from tackler at 0.5 s to contact (P50.05). **Ball-carrier significantliy different from tackler at 0.4 s to

contact (P 5 0.05). #Varsity Cup significantly different fromUnder-19 at 0.5 s to contact (P 5 0.05).


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defender (tackler) interactions. According to Passos

et al. (2008a), in a one-versus-one situation between

attacker and defender, two potential control para-

meters that may affect the outcome in rugby union

are interpersonal distance and relative velocity. The

outcome in this study was characterized by whether

or not contact was made between the attacker and

defender. In the cases where contact was made

(analogous to all the tackles in this study), a critical

period from 4 m of interpersonal distance to contact

(0 m interpersonal distance) was observed. Within

this critical period, contact was predictable when the

defender was able to adjust his velocity so that the

relative velocity was reduced and maintained below 2

m s1 (Passos et al., 2008a). Outside this period,relative velocity did not seem to have much effect

due to players still deciding what action to take (i.e.

to pass, side-step, execute the tackle, etc.) (Passos

et al., 2008a). Applying Passos and colleagues

theory to the present study, a critical period defined

by a specific interpersonal distance and a definitive

relative velocity range before contact may provide a

rationale for our results. The significant differences

outside the 0.3 s time to contact interval for front-on

and side-on tackles in Varsity Cup and Under-19

players, respectively, suggests that these players

probably reach a critical period at this time to

contact interval. Within the subsequent 0.3 s,

tacklers are able to attain a suitable relative velocity

that will afford a tackle on the ball-carrier. Interest-

ingly, no significant differences were found at each

time to contact interval between the ball-carrier and

tackler for front-on and side-on tackles in the Super

14 competition. The differences between ball-carrier

and tackler outside the 0.3 s time to contact interval

in Varsity Cup and Under-19, and the absence of a

significant difference at Super 14, may be indicative

of the standard of play (compared with entering the

tackle at increasing velocities at higher standards, as

we discussed earlier in this section). Tacklers in elite

rugby union may be able to make a decision quicker

and therefore stabilize their velocity sooner to

counterbalance the velocity of the ball-carrier. In

other words, the critical period, specific interpersonal

distance, and definitive relative velocity range may

change according to playing standard and circum-

stance. A more comprehensive analysis studying the

relative velocity in contact and non-contact situa-

tions is warranted to substantiate this.

For all competitions, the mean velocity of the ball-

carrier at each time to contact interval and overall

average velocity is comparable to the velocities of the

ball-carrier studied under controlled conditions. In

contrast, the mean velocities of the tackler seem

higher than tackler velocity measurements recorded

in controlled settings. This is not surprising, how-

ever, since the present study measured the move-

ment velocity of the tacklers upper body. The

rationale for this is that during most tackles, tacklers

enter the tackle with their upper body as the first

point of contact. Also, as pointed out in the

introduction, velocity measurements in control

settings may be limited. The large standard devia-

tions and range of velocities in the present study may

arguably represent the dynamic and variable nature

of the tackle in competitive match-play. In addition,

it may also be a representation of players ability to

adapt their movement velocity in accordance with

their situation. However, since the present study did

not characterize the tackle or tackle situation, no

definitive conclusions can be reached in this regard.

The purpose of this study was to investigate two

variables velocity and acceleration for the ball-

carrier and tackler in three different competitions.

Although this was achieved, there are noteworthy

limitations. Perhaps the most noteworthy limitation

is the sample size of each group. This limitation

could have been avoided had we analysed 60 tackles

of a single group, using one type of tackle. However,

given the importance of the tackle in rugby union at

all levels, and the lack of published data on the

velocity and acceleration profiles of the ball-carrier

and tackler during match-play, we chose the present

study design. Also, the velocity and acceleration of

two types of tackles in three competitions affords the

necessary insight into the current velocity and

Table II. Average acceleration for ball-carrier and tackler before contact during the front-on and side-on tackle in Super 14, Varsity Cup, and

Under-19 competition (mean + s).

Front On Side On

Ball-carrier (m s2) Tackler (m s2) Ball-carrier (m s2) Tackler (m s2)

Mean SD Mean SD Mean SD Mean SD

Super 14 1.24 4.88 1.62 9.62 1.26 8.67 2.44 10.12

Varsity Cup 1.98* 4.95 6.49* 10.64 0.95 9.99 5.28 6.30

Under-19 0.76 8.56 2.65 8.84 2.02 6.24 2.67 3.59

*Ball-carrier significantliy different from tackler (P 5 0.05).


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acceleration profiles of ball-carriers and tacklers in

competitive matches. This insight now provides the

necessary basis for future studies. Even though ten

tackles in each group may limit the generalization of

the results, we consider ten tackles representative of

each competition, as the velocity and acceleration

may not differ greatly should the sample size

increase. Similar to most tackle velocity studies,

this study generally treated the ball-carrier and

tackler as single entities. Although we tried to control

for this by tracking from the upper body of the tackler

and mid-section of the ball-carrier, velocity measure-

ments of individual body parts just before contact

would provide much more insight into the dynamics

of the tackle. For example, although a ball-carriers

velocity is 5 m s1 before contact, the velocity of hisfend (an effective push manoeuvre) can be 10 m s1.The 2D-axis system may also contain a small amount

of artefact since the measurement plane was posi-

tioned at field level, and the player was measured at a

point above the field level. Furthermore, we assumed

that the ball-carrier and the tackler generally main-

tained a linear path of motion over the 0.5 s

period towards the contact. Given these limitations

of the 2D-axis system, it is possible that small

changes in direction such as subtle evasive man-

oeuvres by the ball-carrier, or fine technique

positioning by the tackler just before contact, that

may have had an influence on velocity measurement

were obscured.

Using an innovative video analysis method, the

velocities at which ball-carriers and tacklers in Super

14, Varsity Cup, and Under-19 competitions enter

front-on and side-on tackles during match-play is

now known. While the evidence is not conclusive,

the current study suggests that when tacklers enter

the pre-tackle phase at a velocity considerably

different to that of the ball-carrier (whether higher

or lower), tacklers adjust their velocity accordingly to

reach a suitable relative velocity before making

contact with the ball-carrier. This insight into the

physical components of the tackle in competitive

matches, which arguably govern the dynamics of the

tackle, provides a basis for future studies. Further

research characterizing the tackle, the tackle situa-

tion, and tackle outcome in relation to pre-tackle

velocity and acceleration is recommended for a more

comprehensive understanding of tackles in competi-

tive matches. This understanding will prove invalu-

able for developing effective training strategies for

injury prevention and performance.

Acknowledgements

The authors would like to thank the National

Research Foundation/German Academic Exchange

Service, Medical Research Council of South Africa,

Frank Foreman Scholarship, Glickman/Elliot Scho-

larship, University of Cape Town Equity Scholar-

ship, Doctoral Research Scholarship, and the

Exercise Science and Sports Medicine Scholarship

for support during the study.

References

Alcock, A., Hunter, A., & Brown, N. (2009). Determination of

football pitch locations from video footage and official pitch

markings. Sports Biomechanics, 8, 129140.

Barris, S., & Button, C. (2008). A review of vision-based motion

analysis in sport. Sports Medicine, 38, 10251043.

Bland, J. M., & Altman, D. G. (1986). Statistical methods for

assessing agreement between two methods of clinical measure-

ment. Lancet, 1, 307310.

Brault, S., Bideau, B., Craig, C., & Kulpa, R. (2010). Balancing

deceit and disguise: How to successfully fool the defender in a 1

vs. 1 situation in rugby. Human Movement Science, 29, 412425.

Brewin, M., & Kerwin, D. (2003). Accuracy of scaling and DLT

reconstruction techniques for planar motion analyses. Journal of

Applied Biomechanics, 19, 7988.

Carling, C., Bloomfield, J., Nelsen, L., & Reilly, T. (2008). The

role of motion analysis in elite soccer: Contemporary perfor-

mance measurement techniques and work rate data. Sports

Medicine, 38, 839862.

Correia, V., Araujo, D., Craig, C., & Passos, P. (2011).

Prospective information for pass decisional behavior in rugby

union. Human Movement Science, 30, 984997.

Duthie, G. M., Pyne, D. B., Marsh, D. J., & Hooper, S. L. (2006).

Sprint patterns in rugby union players during competition.

Journal of Strength and Conditioning Research, 20, 208214.

Edgecomb, S. J., & Norton, K. I. (2006). Comparison of global

positioning and computer-based tracking systems for measuring

player movement distance during Australian football. Journal of

Science and Medicine in Sport, 9, 2532.

Fuller, C. W., Ashton, T., Brooks, J. H. M., Cancea, R. J., Hall, J.,

& Kemp, S. P. T. (2010). Injury risks associated with tackling

in rugby union. British Journal of Sports Medicine, 44, 159167.

Gabbett, T. J. (2008). Influence of fatigue on tackling technique in

rugby league players. Journal of Strength and Conditioning

Research, 22, 625632.

Gabbett, T. J. (2009). Physiological and anthropometric correlates

of tackling ability in rugby league players. Journal of Strength and

Conditioning Research, 23, 540548.

Gabbett, T., & Kelly, J. (2007). Does fast defensive line speed

influence tackling proficiency in collision sport athletes?

International Journal of Sports Science and Coaching, 2, 467472.

Gabbett, T., & Ryan, P. (2009). Tackling technique, injury

prevention, and playing performance in high-performance

collision sport athletes. International Journal of Sports Science

and Coaching, 4, 521533.

Garraway, W. M., Lee A. J., Macleod, D. A. D., Telfer, J. W.,

Deary, I. J., & Murray, G. D. (1999). Factors influencing tackle

injuries in rugby union football. British Journal of Sports

Medicine, 33, 3741.

Grant, S. J., Oommen, G., McColl, G., Taylor, J., Watkins, L.,

Friel, N. et al. (2003). The effect of ball carrying method on

sprint speed in rugby union football players. Journal of Sports

Sciences, 21, 10091015.

Hendricks, S., & Lambert, M. (2010). Tackling in rugby:

Coaching strategies for effective technique and injury preven-

tion. International Journal of Sports Science and Coaching, 5, 117

135.

Hendricks, S., Jordaan, E., & Lambert, M. (2012). Attitude and

behaviour of junior rugby union players towards tackling during

training and match play. Safety Science, 50, 266284.


Dow

nloa

ded

by [T

he U

nivers

ity of

Wes

t Lon

don]

at 11

:21 13

June

2015

Jennings, D., Cormack, S., Coutts, A. J., Boyd, L., & Aughey, R.

J. (2010). The validity and reliability of GPS units for

measuring distance in team sport specific running patterns.

International Journal of Sports Physiology and Performance, 5,

328341.

Kwon, Y. H., & Casebolt, J. B. (2006). Effects of light

refraction on the accuracy of camera calibration and recon-

struction in underwater motion analysis. Sports Biomechanics, 5,

95120.

Mallo, J., Veiga, S., de Lopez, S. C., & Navarro, E. (2010).

Activity profile of top-class female soccer refereeing in relation

to the position of the ball. Journal of Science and Medicine in

Sport, 13, 129132.

McIntosh, A. S., McCrory, P., & Comerford, J. (2000). The

dynamics of concussive head impacts in rugby and Australian

rules football. Medicine and Science in Sports and Exercise, 32,

19801984.

McIntosh, A. S., Savage, T. N., McCrory, P., Frechede, B. O., &

Wolfe, R. (2010). Tackle characteristics and injury in a cross

section of rugby union football. Medicine and Science in Sports

and Exercise, 42, 977984.

Meir, R. (2005). Conditioning the visual system: A practical

perspective on visual conditioning in rugby football. Strength

and Conditioning Journal, 27, 8692.

Mouchet, A. (2005). Subjectivity in the articulation between

strategy and tactics in team sports: An example of rugby. Italian

Journal of Sport Sciences, 12, 2433.

Nevill, A. (1996). Validity and measurement agreement in sports

performance. Journal of Sports Sciences, 14, 199.

Nevill, A. M., & Atkinson, G. (1997). Assessing agreement

between measurements recorded on a ratio scale in sports

medicine and sports science. British Journal of Sports Medicine,

31, 314318.

Pain, M. T., Tsui, F., & Cove, S. (2008). In vivo determination of

the effect of shoulder pads on tackling forces in rugby. Journal of

Sports Sciences, 26, 855862.

Passos, P., Araujo, D., Davids, K., Gouveia, L., Milho, J., &

Serpa, S. N. (2008a). Information-governing dynamics of

attackerdefender interactions in youth rugby union. Journal

of Sports Sciences, 26, 14211429.

Passos, P., Araujo, D., Davids, K., Gouveia, L., & Serpa, S.

(2006). Interpersonal dynamics in sport: The role of artificial

neural networks and 3-D analysis. Behavior Research Methods,

38, 683691.

Passos, P., Araujo, D., Davids, K., Gouveia, L., Serpa, S., Milho,

J. et al. (2009). Interpersonal pattern dynamics and adaptive

behavior in multiagent neurobiological systems: Conceptual

model and data. Journal of Motor Behavior, 41, 445459.

Passos, P., Araujo, D., Davids, K., & Shuttleworth, R. (2008b).

Manipulating contraints to train decision making in rugby

union. International Journal of Sports Science and Coaching, 3,

125140.

Quarrie, K.L., & Hopkins, W. G. (2008). Tackle injuries in

professional rugby union. American Journal of Sports Medicine,

36, 17051716.

Sekiguchi, A., Yokoyama, S., Kasahara, S., Yomogida, Y.,

Takeuchi, H., Ogawa, T. et al. (2011). Neural bases of a

specific strategy for visuospatial processing in rugby players.

Medicine and Science in Sports and Exercise, 43, 185762.

Walsh, M., Young, B., Hill, B., Kittredge, K., & Horn, T. (2007).

The effect of ball-carrying technique and experience on

sprinting in rugby union. Journal of Sports Sciences, 25, 185192.

Watson, G., Brault, S., Kulpa, R., Bideau, B., Butterfield, J., &

Craig, C. (2011). Judging the passability of dynamic gaps in

a virtual rugby environment. Human Movement Science, 30,

942956.

Wheeler, K. W., Askew, C. D., & Sayers, M. G. (2010). Effective

attacking strategies in rugby union. European Journal of Sport

Science, 10, 237242.

Wheeler, K., & Sayers, M. (2009). Contact skills predicting tackle-

breaks in rugby union. International Journal of Sports Science and

Coaching, 4, 535544.

Wheeler, K. W., & Sayers, M. G. L. (2010). Modification of agility

running technique in reaction to a defender in rugby union.

Journal of Sport Science and Medicine, 9, 445451.

Wilson, B. D., Quarrie, K. L., Milburn, P. D., & Chalmers, D. J.

(1999). The nature and circumstances of tackle injuries in

rugby union. Journal of Science and Medicine in Sport, 2, 153

162.


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velocity and acceleration before contact in the tackle during rugby union matches

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