She put her hands on him first. You need to watch the video - not the .gifs.
He tries to get into the bar. He puts his hand on the open space (probably to claim a spot) and there is some contact with the white girl and the other girl leaving the bar. It's really crowded, so this type of contact is expected.
Girl gets offended by this, and moves over to the left a little bit to get into his way. It kinda looks like she throws a hip/butt at him a bit. That's where the confrontation starts. She turns around, puts her left hand on his chest and raises her right hand in a fist. He restrains her and pushed her back. She knees him or kicks him, then punches. There is some other chick off screen also throwing her hands at him.
He punches her once and leaves. She has a bloody nose (any other damage?). She leave the bar with friends.
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I don't think he used excessive force. IMO not sure why the authorities had to get involved in this one, but OK. I can understand his school punishing him (he is underage, at a bar, getting in fights) but if I were on the jury I would not think he should get any legal punishment.