Riots following big sporting events have become predictable. They happen about half the time following a championship game or series, the experts say.

What's more, sports riots are now the most common type of riot in North America.

But they are usually celebratory sports riots. What makes Vancouver stand out, both in 2011 and 1994, is that its street mayhem followed the home team losing the big game.

In fact it is so unusual that Jerry Lewis, the author of Sports Fan Violence in North America, told CBC News that what we saw Wednesday night "might be called the Vancouver effect."

An emeritus professor of sociology at Kent State University in Ohio, Lewis has looked closely at over 200 sports riots in the U.S. and none of them followed a loss by the home team.

The vast majority of sports riots in North America are celebration riots. Los Angeles Lakers fans jump over a fire in the street in celebration after the Lakers won the NBA championship on June 15, 2001. (David McNew/Getty Images)That little quirk aside, however, Vancouver's night of rampage does fit relatively well with the overall pattern of sports riots in North America. From his research, Lewis has identified five common conditions:

• A natural urban gathering place.
• The availability of a 'cadre' of young, white males.
• Championship stakes.
• Deep in the series.
• A close, exciting game.

All but the last condition applied to Vancouver on Wednesday, game seven of the Stanley Cup finals. Boston had scored three goals in the second period and then added an empty netter late in the third.

Different in Europe

The situation is different in Europe. The European-style riot, which has been the scourge of politicians there for years, has fans fighting each other and is usually initiated by the losing team's supporters.

On both sides of the Atlantic, however, alcohol often acts as an accelerant.

Bob Carrothers, a social psychologist from Ohio Northern University, also studies sports riots and, expecting the likelihood of an outburst following a seventh game of a Stanley Cup series, he was closely monitoring the events in Vancouver.

His take was that the Vancouver situation followed "a very European pattern where a loss almost seems like an attack on your identity, on your city, on your team, on who you are."

He said that in North America, mostly "when your team loses, you feel bad, you slink home and you pout."

From what we know about the Vancouver outburst there was no clear triggering event after the game. But, according to Lewis, that is consistent with many other sports riots.

Identifying with your team

In his examination of the subject, Lewis says rioting by fans is a manifestation of a strong identification with the team.

While the fan can't contribute on the ice or playing field, he says "the act of violence becomes an analogy to the sports skill of the hockey players in a celebrating riot."

Riots in Vancouver followed both times the Canucks lost the seventh game of a Stanley Cup final. Members of a large crowd in downtown Vancouver disperse after being tear gassed by police June 14, 1994. Riot police moved in after rioting started following the Vancouver Canucks loss against the New York Rangers in the Stanley Cup final in New York. (Chuck Stoody/Canadian Press)

The irony of the Vancouver riots, of course, is that they were not celebrations of victory.

Both Lewis and Carrothers told CBC News that they think the post-game rioting in Vancouver was simply an expression of frustration.

The usual explanation for youth violence — alienation — does not seem to be a factor in sports riots, Carrothers feels. In this case, fans are identifying with a community and with their team.

Carrothers did say that compared to other sports riots, the level of violence in Vancouver was very strange, "almost like there's an outside force."

Vancouver police Chief Jim Chu described the instigators as anarchists and criminals and he said they appeared to be the same people involved in the demonstrations leading up to the Winter Olympics.

Sports riots vs. political riots

Compared to political riots, like the kind we've been seeing in Greece for weeks now, sports riots tend to be much shorter. Lewis found that they typically last two to three hours while political riots, including race riots, go on longer, sometimes for days and weeks at a time.

Another difference is that, while the key variables for sports riots are young males, in political riots women also participate.

Lewis pointed out that another difference is that political riots have very clear perceived causes. But with sports riots, as Carrothers said in our interview, "I don't know that in their minds, there is even an achievement part to it, it's really just an emotional release."

Leading social scientists like Mancur Olson, Charles Tilly and Sidney Tarrow in their studies presented political protests as performances.

In what they call contentious politics, there is a very small core group of leaders, a larger intermediate group that follows them, and a much larger group still that gets caught up in the action in order to make a political point, or bring about change.

Sports riots can be interpreted in a similar way, some say.

Vancouver Canucks watch a car burn during a riot following game 7 of the NHL Stanley Cup final in downtown Vancouver on June 15. Riots following losses are so unusual, it might be called the Vancouver effect, sociologist Jerry lewis told CBC News. (Geoff Howe/Canadian Press)

In Lewis's analysis, "the active core are not necessarily rational leaders who are politically concerned but are simply people who start doing violent behaviour."

"Young white males just start doing it, there's a gathering around them of what I call cheerleaders who act in support, then the observers create an arena," Lewis explained.

Carrothers said that appeared to be the case in Vancouver, even though it was not a celebrating event.

"Vancouver might just be an international city with a different dynamic," he said, adding, "It's nothing they should be ashamed of as a city, it happens."

Lewis's conclusion is that the 'Vancouver effect' is completely different from other sports riots. "We have to figure out why."

With files from Roland Lindala-Haumont and Ali Mustafa