What turn a crowd into a mob

What turn a crowd into a mob, i think it is when the controller of these people was doing a really really bad job, like taiwan always have these kind of things, and the Chicago teacher also done this kind of thing few weeks ago. And when a person that has something that the everyone else that didn't have, i will prop ally turn a crowd into a mob, like their are many movie that happens these kind of things, like War of the Worlds, when the main characters drove a car throw a crowd of people that don't have a car and they also want to run away from aliens, the crowds all come up and hit the car, even at last they use a gun. And at last, when their was someone in a group that was scary, people often will first pick the one that was weird, but unforchunnaly they were often wrong, so there is where the fight begins.