Something happened around the 7 second mark that made her look back to figure out who this guy was tight up against her. Then something happened to make her spin around (14 second mark), put a forearm on his chest and ball up her fist and run her mouth at him. What that something was, I'm not sure, but it appears that she takes offense at him bumping into her. Maybe he was trying to force his way to the bar and she'd had enough, or was intoxicated and lost her sense of patience. Who knows.

So when she stood up to him, he grabbed her arm and pushed her back enough to bang into the guy next to her in the glasses (18 second mark). She has her leg up too, trying to push him off of her...i'm not a lip reader, but it looks like she is saying "Hey Hey!" ...then a reques to let go of her arm. He didn't...so she threw a very soft punch. BAM..he ended that confrontation.

What I notice is at the 23secnd mark, he's punching her. At the 25 second mark, he is long gone. He knew he wasn't in the right, so he bolted.

Guy was the aggressor. He was the one behind her doing something that made her spin around. He grabbed her arm and shoved her back. He wouldn't let go. Girl didn't help herself though either by mouthing off and throwing a punch herself...but when someone will not let you go--it is understandable. Guy lost control and rocked her face. His fault.