Here's a strange video of a man beating up a fellow passenger shot through the window of a subway car. According to the description of the video, the fight (if you can call one dude getting beat about the head and neck repeatedly a "fight") erupted over a dispute over a subway seat.
I'm not sure how the cameraman found that out, considering we only see him trapped outside the car, while the doors won't open and the poor victim just gets beat and beat and beat, with barely anyone to help him. He can't even make a run for it! But he's probably not a poor victim if he's the one who started the fight. Then he's a dick who deservedly got his ass beat. Anyway, anything can happen on those New York City subways, so it's best to just be nice to the other straphangers, now isn't it?