Sports fans are more likely to be aggressive after watching their team win rather than lose, a study suggests.
Match days see a strong police presence in Cardiff
A Cardiff University team quizzed 197 male rugby supporters going in and out of the city's Millennium Stadium.
They found those who had seen their team win or draw were more aggressive than those who had seen their team lose or had been questioned before the game.
Researchers said fans may get caught up by the euphoria of a win and lose perspective, increasing aggression.
The report, published in the Criminal Behaviour and Mental Health journal, also found that the result did not affect planned alcohol intake, which remained similar for all of those questioned.
Losing reduced happiness, but winning did not increase it, the researchers added.
Researchers quizzed 111 supporters as they entered the stadium and 86 as they left.
People were asked about their planned drinking, feelings of happiness and tendency towards aggression.
Lead researcher Simon Moore said: "The results are consistent with events around the world which have seen the fans of winning teams run riot after the match.
"A possible explanation could be that if a supporter's team wins or draws, he can get so caught up in the match that he loses sight of the future and this loss of perspective leads to increased aggression."
Marc Jones, of the British Psychological Society, said: "In many ways the findings are surprising because you would expect the opposite - for supporters of the losing team to be more aggressive.
"Frustration, which is associated with losing, can cause aggression. But I think it will be worth looking at the physiological reaction to winning.
"It is known that winning causes an increase in testosterone, which has been associated - although far from established - to increases in aggression."