Totally fake. Just watch her. When he comes towards her she stops and winds up and waits for him to grab her ass then hits him. It'd be funny if I saw that for real though lol.
So hard not to believe videos like this are fake since they often are, but I'm not buying "fake" quite yet. Not enough back story info. Did he know her? Was he drinking? Had he harassed her prior to where the video starts?