Why Some Sports Fans Turn to Vandalism Even After a Win

San Francisco police donned riot gear to control rowdy fans after Giants' win.

“This is not uncommon after many major sporting events,” said Brad Bushman, a professor of communication and psychology at the Ohio State University School of Communication.

People who feel they have “won” sometimes like to boast or celebrate that victory, he said, though the victory can end with their trying to diminish the loser in order to feel better.

“Social identity theory shows that people like to take pride in the groups they belong to,” Bushman said. “But often people think to make themselves feel better they have to stomp down those who belong to other groups.”

After the Giants won the World Series for the third time in five years, some of their fans took to the streets immediately after the game near the baseball stadium where the team plays to celebrate with cheers and in some cases property damage.

The celebrations turned violent and destructive in some cases with two people shot and one person stabbed, according to The Associated Press. Police told the AP that bottles were thrown at police and multiple officers had minor injuries, amid people setting bonfires, painting graffiti and igniting fireworks.

Police in riot gear took to the streets and used tear gas to get fans to disperse.

Forty people were arrested Wednesday night, according to the San Francisco Chronicle, which reported this afternoon that police said three people were booked for alleged assault and two for illegal gun possession.

Police said many of those arrested were from outside San Francisco.

One local merchant, Kim Jung, 57, complained to the newspaper about the graffiti scrawled outside his diner. “I’m lucky there wasn’t any broken windows,” he said.

Speaking of the vandalism, he asked, “Why is it like that?”

Experts cite crowds as a contributing factor, saying anonymity allows people to feel like they can do something illegal or dangerous and not be caught.

"It’s a group contagion effect," said Stanley Teitelbaum, a psychologist and psychotherapist in New York. "When they’re part of a group, then they’re more prone and more likely to join in and let that aggressive side of themselves."

Teitelbaum said an intense game, like the final game at the World Series, can result in people searching for a release through destructive behavior.

"Internally, people are psychologically and emotionally building up a lot of intensity and tension," he said. "It becomes an opportunity or an excuse to let all this out."

Teitelbaum said people may start out thinking they're doing something minor, but that it can quickly spiral out of control.

"You start to rock a car and you don’t’ necessarily mean to get it turned over," Teitelbaum said. “You’re expressing an aggressive feeling."

While a World Series win can lead to heightened emotions, they're not always positive, according to experts.

Fredrick Koenig, former professor of social psychology at Tulane University in New Orleans, said for some people extreme happiness can turn into extreme aggression.

“This is an aspect of crowd behavior and it’s called ‘excitation transfer’; one part of your brain gets excited and it transfers over to aggression,” Koenig told ABC News.

Koenig said if the excitement transmits to aggression, being in a crowd with a lot of other like-minded people is not a good place to be.

"In crowds the rules aren’t there anymore; [people] start doing things that are not normative," he said.