Sudden Chaos

''That guy just punched another guy! Time for us to lose it!''

For some weird reason, whenever one person hits another person in a crowded area, like at a baseball game, that's a sign everyone else "should" do the same without any real reason for doing so. The thing that makes everyone shut up is The Thing That Makes Everyone Shut Up.

This is under Violence Because Violence since the two are essentially the same thing, but Violence Because Violence is a little broader than Sudden Chaos.