This is the first time that the impact of slow motion video on decision making has been studied in sports referees and it is timely given the current debate on video assistant refereeing (VAR), which will be used in the World Cup in Russia.
They found no significant difference in the accuracy of a referee's decision about whether a foul had occurred or not, with slow-motion videos (63 per cent accurate) compared to the real-time videos (61 per cent accurate).
However, the judgement of intention or force behind a foul differed. More red cards were given by referees watching in slow motion compared to those watching real time video playbacks.
"Our results suggest that slow motion can increase the severity of a judgement of intention, making the difference between perceiving an action as careless (no card), reckless (yellow card) or with excessive force (red card)," said Jochim Spitz, a professor at the University of Leuven.
"The finding that referees were more likely to make more severe decisions following slow motion replays, is an important consideration for developing guidelines for the implementation of VAR in football leagues worldwide," Spitz said.
The study, published in the journal Cognitive Research: Principles and Implications, concluded that although slow motion playback could be a useful tool in assessing some decisions, such as off-side and determining the exact impact of a contact, it may not be the best tool for decisions that involve judging human behaviour and intention.
"Slow motion video may make it clearer who initiated a foul, whether there actually was contact and whether a foul occurred either inside or outside the penalty area," Spitz said.
"However, judging human emotion, like intentionality is quite another story. It is also the reason why slow motion footage cannot be used anymore in the court room as it increases the perceived intent," he said.
To investigate the impact of viewing speeds on decisions made by referees, the researchers showed 88 elite football referees from five European countries 60 video clips of foul situations from football matches in real time or slow motion.
Two independent ex-international referees that are currently acting as refereeing experts determined the correct decisions as a point of reference and then the referees who took part in the study categorised the fouls as they would in a real match by awarding a yellow card, a red card or no card.
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