Winning, not losing, triggers violence among supporters after a sports match, a study suggests.
Match days see a strong police presence
Welsh researchers found more victims of assault were treated at Cardiff's A&E department after Wales won at rugby or football than if they had lost.
The same was true even if the national teams were playing away.
Writing in the journal Injury Prevention, the researchers say alcohol is a major factor - and add their findings should help prevent violence.
Cardiff has a population of about 300,000, and international rugby and football matches often attract in excess of 70,000 fans.
A team from the Violence Research Group at Cardiff University looked at the number of assault cases seen at the city's only casualty department between May 1995 and April 2002.
The unit is about a mile from the national stadium.
Home and away
During this time, 106 home and away fixtures took place - 74 rugby matches and 32 football matches.
Almost 27,000 assault cases required emergency treatment over the course of the study.
On average, 30 cases of assault required medical attention on the day of the match and the day after.
On days when no match had been played, the average number of assault cases fell to 21.
But whether the matches were played at home or away had little impact on assault rates.
When Wales won, the average number of assault injuries seen was 33. When the team lost, the average dropped to 25.
Writing in Injury Prevention, the team led by Dr Vaseekaran Sjvarajasingam, said: "When the national team played in another country the population was affected by the outcome to the same significant extent as the population on home match days.
"Winning prompts celebration, a key component of which is alcohol consumption, and prompts the formation of crowds of intoxicated individuals, making interpersonal physical assertiveness more likely."
The researchers said a win may also boost levels of self confidence, assertiveness or patriotism, all of which could lead to violence.
Other research has shown that domestic violence occurs more often when the male assailant's local team wins.
Paul Mathias, a former chief superintendent in the Metropolitan Police who now works as a psychologist, said: "There was a significant rise seen in assaults and other acts of violence or abuse on match days.
"But it's not clear whether these were people who had been at the match or watching it at home."