Judging offside in football

1
Judging offside in football

• Journal Club, 2006

2
Errors in judging offside in football.
Oi Lino are you blind?
3
Law 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

4
Offside
Onside
5
Oudejans 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

6
Cause 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

7
Farside
8
Farside
FE/NFE 171/31
9
Farside
FE/NFE 21/43
FE/NFE 171/31
10
Nearside
11
Nearside
FE/NFE 34/16
12
Nearside
FE/NFE 19/84
FE/NFE 34/16
13
Conclusions

• FE bias when attackers go left.
• NFE bias when attackers go right.
• Errors caused by relative optical projections of
  players on ARs retina.
• AR limited by their perceptual systems (or
  positioning systems!).
• Off-line analysis of video images from adequate
  observation point.

14
Baldo et al (2002) - Perception

• Reanalysis of Oudejans et als 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)

15
Flash-lag effect
16
Flash-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

17
Geometric effect
NFE
FE
18
Geometric effect Flash-lag effect
NFE
FE FL
FE FL
FE
19
Results

• 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 lt (FE/NFE)RT.
• (65/266)LT lt (58/175)RT.

20
Conclusions

• 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.

21
Issues

• 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)?

22
(No Transcript)