The guy in the crowd stole something from her (a bracelet I think) so she punched him.
You know i've watched a couple of youtube clips now and can't see her wearing a bracelet on any of them. Might be a small one that you can't see or something.
Or, she's a whacked out traincrash who thought someone in the crowd was doing something they were not, because she's so messed up she's not really aware of whats happening around her.
You be the judge....