Judging offside in footballJudging offside in football

Journal Club, 2006

Errors in judging ‘offside’ in football.Errors in judging

‘offside’ in football.

Oi Lino – are you blind?

Oi Lino – are you blind?

Law 11: OffsideLaw 11: Offside A player is in an offside position if he is nearer to

his opponents goal line than both the ball and the second last opponent

A player in an offside position is only penalised if, at the moment the ball touches or is played by one of his team, he is, in the opinion of the referee involved in active play by: interfering with play interfering with an opponent

OffsideOffsideOnsideOnside

Oudejans et al (2000) - NatureOudejans et al (2000) - Nature Claim angle of viewing by assistant referee

leads to inevitable optical errors. 3 assistant referees. 200 offside judgements - 40 errors. ARs cannot see passer and receiver

simultaneously. ARs 1.2m ahead of offside line on average

Cause of errorCause of error One hypothesis:

AR shifts gaze from passer to receiver Alternate hypothesis:

Misalignment of AR and last defender (1.18m) Flag error (FE) - receiver wrongly perceived as

ahead of last defender No flag error (NFE) - receiver wrongly

perceived as behind last defender

FarsideFarside

FarsideFarside

FE/NFE: 171/31

FarsideFarside

FE/NFE: 171/31

FE/NFE: 21/43

NearsideNearside

NearsideNearside

FE/NFE: 34/16

NearsideNearside

FE/NFE: 34/16

FE/NFE: 19/84

ConclusionsConclusions FE bias when attackers go left. NFE bias when attackers go right. Errors caused by relative optical projections of

players on AR’s retina. AR limited by their perceptual systems (or

positioning systems!). Off-line analysis of video images from adequate

observation point.

Baldo et al (2002) - PerceptionBaldo et al (2002) - Perception Reanalysis of Oudejans et al’s data. Proposed that flag errors due to flash-lag

effect rather than geometrical/optical effect.

Flash-lag effect: A moving object is perceived as spatially

ahead of its real position at an instant defined by a time marker (e.g. a flash)

Flash-lag effectFlash-lag effect

Flash-lag model for footballFlash-lag model for football

Moving object: the receiver running towards goal.

Time marker: the moment that the passer kicks the ball.

This effect adds to the geometric/optical effect, leading to an overall bias towards FE than NFE

Geometric effectGeometric effect

NFE

FE

Geometric effect + Flash-lag effectGeometric effect + Flash-lag effect

NFE

FE

FE + FL

FE + FL

ResultsResults

FE/NFE ratio was 324/240 Asymmetry in left & right trajectories (FE

bias for left in geometric/optical effect). Flash-lag effect predicts increase in FE for

both left & right trajectories: (NFE/FE)LT < (FE/NFE)RT.

(65/266)LT < (58/175)RT.

ConclusionsConclusions Flash-lag contributes to an existing

geometric/optical effect. Other factors may contribute (over-

zealousness, FIFA recommendations etc.). Flash-lag errors could also occur when the

AR is in alignment with the offside line. Bridge between lab and field needs to be

made.

IssuesIssues Eagleman: flash-lag occurs when flash & moving

object appear in same location. Can FL occur when flash is in peripheral? Variance in relationship/distance between

attacker & defender (e.g., far/near)? Gaze shift hypothesis rejected after examination

of 1 AR! No gaze shift - how do ARs fulfil other

responsibilities (e.g., throw-in)?