Football fouls more likely to be given when play heads left

A simple perceptual bias could influence football referees' judgements about whether a foul occurred or not. That's according to Alexander Kranjec and colleagues, who had 12 football players at the University of Pennsylvania look for half a second each at 268 static images of one player tackling another and decide whether a foul had been committed. Unbeknown to the participants, 134 of the pictures were simply mirror opposites of the other 134.

The key finding was that more fouls (66.5 vs. 63.3 - a statistically significant difference) were judged to have occurred when assessing the images in which movement was captured in a leftward direction than when assessing the same images mirror-reversed and therefore featuring implied rightward motion. The researchers think this anomaly may have to do with our bias (at least in cultures that read from left to right) for rightward motion. Motion from right to left is perceived as less natural and this may be responsible for influencing judgements about fouls during play in that direction. Apparently film directors exploit this same bias by having villains arrive on-screen from the right.

Kranjec's team said their finding has implications for refereeing. The most popular system, known as the 'left diagonal refereeing system' (see picture), in which the referee runs a diagonal axis between the two left-hand corners of the pitch, results in the referee witnessing tackles in both goal areas primarily from a right-to-left perspective, thus making judgments of fouls in these areas more likely - an advantage to attackers. This is okay because it applies to both teams. What's important, Kranjec and colleagues warn, is that the referee doesn't switch to a 'right diagonal system' half-way through a match, potentially penalising a losing side that needs to attack yet no longer enjoys the benefits of this perceptual bias when playing in offensive areas.

'These results ... suggest that the effects of a low-level perceptual mechanisms could alter a decision, change the result of a game and perhaps, the fortunes of nations,' the researchers said.
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Kranjec A, Lehet M, Bromberger B, & Chatterjee A (2010). A sinister bias for calling fouls in soccer. PloS one, 5 (7) PMID: 20628648