Sudden Chaos

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

For some weird reason, whenever one guy hits another guy in a crowded area, that's a sign everyone else should do the same without any real reason for doing so. The only thing that can calm everybody down is The Thing That Makes Everyone Shut Up.

Put this under Violent Because Violence since the two are pretty much the same thing, but Violent Because Violence is a little broader than Sudden Chaos.