When things go amuck, they are wildly out of control. Someone running amuck is showing no self-control.
This is a word that has to do with chaos and disorder. A riot is an example of people running amuck. In a cafeteria, if people are yelling and throwing food, they are going amuck. This word applies to times when control has been lost: people are showing no self-control, and the situation is out of hand. Sometimes, going amuck is positive, though. If a football player scores five touchdowns in a game, you could say he's running amuck.