Given the current debate on video assistant refereeing (VAR), which will be used in this year's World Cup matches in Russia, a new study warns that football referees penalise situations more severely when watching them in slow motion compared to real time.
The researchers found no significant difference in the accuracy of a referee's decision regarding whether a foul had occurred or not, with slow-motion videos (63 percent accurate) compared to the real-time videos (61 percent 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, showed the findings published in the journal Cognitive Research: Principles and Implications.
"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," said one of the study authors Jochim Spitz from University of Leuven (KU Leuven) in Belgium.
"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 courtroom as it increases the perceived intent," Spitz added.
For the study, the researchers studied the response of 88 elite football referees to video clips of a foul warranting a yellow card.
"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).
"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 added.
The authors 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.
At a press conference on Saturday, Massimo Busacca, head of FIFA's refereeing department, said the VAR would be important at the World Cup but stressed that the officials on the field would still be tasked with managing the games.
"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," Spitz added.