When close to 3,000 people gathered in what became a riot near Minnesota State University, Mankato, only a few of those present overturned cars and started fires. Most just stood by and watched.

But people who have studied student riots say spectators are as culpable as those who destroy property. Some schools are beginning to acknowledge that in discipline policies.

The University of Minnesota's student conduct code, passed in June, gives school officials the power to discipline not only students who destroy property during an off-campus riot, but those who block traffic or refuse to leave when police order them to.

Jim Franklin, Mankato's director of public safety, said crowd behavior encouraged destruction this past weekend in a residential area near campus. When the undermanned police force pulled back at one point because it did not want to push the crowd onto campus or into another neighborhood, people began chanting, "We won, we won."

The 45 people who were eventually arrested, Franklin said, "were the drunkest and the stupidest" who stayed until the bitter end.

Many people refused to leave when police ordered them to.

"We have had calls here saying, `I didn't do anything, and I was hit with spray or pepper balls,"' Franklin said. "I would say, `You should not have been there.' ... When the word is to break it up, it means go home, get out of here."

At both the Mankato riot and the melee that followed the University of Minnesota's NCAA hockey championship in April, people in the crowd used cell phones to bring more people to the scene, treating the situation as an event. Last spring, students at the university reported overhearing other students talk about "next year's riot," as if it were a college ritual to be repeated year after year.

"I put the onus as much on the onlookers and the crowd as I do on the person swinging the bat," said Daniel Wann, psychology professor at Murray State University in Kentucky. "People don't do what they do without 3,000 people egging them on."

Raymond Montemayor, a professor of psychology at Ohio State University, said crowds create "pressure to be part of it. ... A lot happens because a lot of people are watching. ... The audience starts clapping and yelling and it all seems like fun. Most of these kids are not truly antisocial. They're swept up by the situation."

At Ohio State, which had a riot near campus after a 2002 football game against Michigan, students "didn't seem to understand that when police tell you to disperse, that's an order," Montemayor said. "Just being in the area is a violation."