Some people in the stands turn into monsters during sporting events.

This is the incident that pretty much convinced me not to go to sporting events (except The Globetorrters):
http://www.espn.com/los-angeles/mlb/story/_/id/10489372/two-men-admit-guilt-dodger-stadium-attack-bryan-stow

At least dude is doing better, but he's still fucked:
http://www.cnn.com/2016/05/13/health/bryan-stow-san-francisco-giants-fan-rewind/