I don't care what led up to this, this man is despicable. Unless you're trying to protect yourself from a woman trying to kill you with a knife or a gun, you should NEVER punch a woman. Especially when she's not even posing a threat!
The video starts with someone saying, "She just walked right up and punched him", but the situation seems to be somewhat controlled with other people holding her back. She allegedly (and it looks like it) spits on the guy, when he blindside steps in and punches her. Hard.
Just walk away. WALK. AWAY.