The researchers base their findings on the numbers of people requiring emergency medical treatment for assault at the time of international rugby and football matches in one capital city (Cardiff) in Wales.
With a population of 300,000, Cardiff is the largest city in Wales. International rugby and football matches are the most popular spectator sport in Wales, and matches often attract in excess of 70,000 fans.
The research team tracked the number of assault cases presenting to the only emergency medicine department in Cardiff between May 1995 and April 2002. The emergency medicine facility is about a mile from the national stadium.
During this time, 106 home and away matches took place:74 rugby matches and 32 football matches. And almost 27,000 assault cases required emergency treatment.
On average, 30 cases of assault required medical attention on the day of the match and the day after. Attendance peaked just before midnight on the day of the match.
On days when no match had been played, the average number of assault cases fell to 21.
When the researchers took into account whether the match was home or away, and won or lost, they found that the result had a significant impact on the figures.
When Wales won its matches, the average number of assault injuries seen was 33; when Wales lost, the average dropped to 25. At weekends, the number of assault injuries was also around a third higher when matches were played than when there were no matches. Whether the matches were played at home or away had little impact on the rates. It was the score and match attendance that mattered.
"These analyses suggest that assault may not be the result of negative factors associated with a national team losing, but the result of a positive event (winning)," say the researchers.
A win may also boost levels of self confidence, assertiveness or patriotism, all of which might lead to violence, they add. Other research shows that domestic violence is more likely when the male assailant's local team wins.
Winning is also likely to be associated with the celebratory downing of alcohol, a factor that is well known to increase the risk of violence, they say.