What it looks like to me: they both are trying to make their way to the bar, she gets to the bar first but he sees a space behind a girl who is just standing in front of the bar like an ass, he asks her to move, she tries but hardly moves, he decides to squeeze between the two girls, girl at the bar gets upset at him for forcing her into the bar, turns, and says some words to him with her fist raised and other hand on him, he grabs her wrists to prevent her from swinging, she struggles to get free but when she does she swings at him, he then smacks the hell out of her. Yes, I do think it was actual an open palm hit. His hand is open after contact with her face.
Do I think he's total a dumbass and dick for swinging at her? Yes, but from watching that video, it does look to me like she was the aggressor.
And that being said, me saying "what it looks like to me" is far from me saying "this is totally what happened" so no need to tell me that police and witness reports disagree with me. Besides, who are the witnesses? Nobody was paying any damn attention apparently except another girl who comes to assist the girl who just got hit.
PS - To say his hands were on her before she raises her fist is just wrong. You can clearly see his right and then his left hand on the bar trying to get in and she turns and raises her fist.