Other riots have involved burning buildings and looting stores that had no particular connection to the motivation for the riot. Not all collective behavior is violent, although much of it is. Not all collective behavior is an adverse response to an event, although, again, much of it is. I happened to be in downtown Detroit in 1968 when the Detroit Tigers, playing in the old Tiger Stadium very near downtown, won the World Series just at the close of the business day. The downtown area of the city erupted into a gigantic party involving thousands of people and lasting for about eight hours.
Collective behavior needs both an social environmental context and a stimulus or trigger.
Researchers studying the social context of lynchings of Afro-Americans in the South found that lynchings were more common when the price of cotton was low, putting strains on the economy, than when they were when prices were high. Triggers or stimuli for the expression of collective behavior are the events that create the heightened emotion that leads people to get involved in the collective action. Rumors often play a part in the triggering mechanism. The social context involved the Vietnam War and claims that poor Blacks were disproportionately being drafted because better off whites could go to college and get deferments. It also involved unfulfilled but rising expectations for lower Black unemployment because of the civil rights laws passed a few years earlier.