Sudden Chaos

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

For some strange, illogical 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 only thing that can get everyone to shut up is the Shut-Up Interruption.

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.