Which concept refers specifically to the rapid spread of emotions and behaviors through a crowd by imitation and social influence?

Which combination of preconditions most strongly predicts the risk that an acting crowd will escalate into a mob and then a riot?

A demonstration begins as a coordinated protest targeting a police precinct with demands to be met; after clashes, some participants begin looting unrelated businesses and the group splinters. Which sequence best describes the sociological transition and why?