According to a new study, competitive team sports like football or basketball are more likely to turn aggressive when the teams are evenly matched in comparison to contests between two unequal teams.
In a study of premier league football matches in Germany and basketball games in the North American league, researchers of the University of Groningen in the Netherlands have found that aggressive contact between players increases when opponents are more equal, the researchers said.
The same is also true of aggressive contests between individuals in the animal kingdom, whether it is rutting deer stags or quarrelsome Siamese fighting fish.
For their study, Gert Stulp and colleagues of the University of Groningen in the Netherlands counted the fouls in 1,530 football matches in the German Bundesliga and 1,230 games in a season of the National Basketball Association. They gave each team a ranking based on their past performance and this was used to calculate a measure of ability called resource-holding potential (RHP).
According to the scientists, the RHP of each team became a good measure of relative ability compared with other teams in the same league.
"We found that in both sports the number of fouls committed increased when the different in RHP was smaller. Thus we provide what is to our best knowledge the first evidence that, as in conflicts between individuals, conflicts escalate more when the groups are more similar in RHP," the researchers said.
"More specifically, the difference in ranks, that is the difference in our estimate of group RHP between teams predicts the number of fouls committed during a game of both football and basketball.
"Moreover, we found that in football more cards were shown by the referee when differences in rank were smaller, showing that more severe fouls were committed when the difference in RHP was smaller," they added.
Previous research on male football players had shown that the sex-hormone testosterone, which is linked with aggression, increases significantly prior to matches when the game was between two extreme rivals - more so than when playing against a moderate rival.
"Thus playing against a well-matched team may well increase testosterone and hence the aggressiveness of the players, which results in more fouls," the scientists suggested.
The study was published in the journal Biology Letters.