I'm not sure how I feel about this video. I don't want to assume the worse and it's possible that the women may have been having a bad day or on drugs or something else (I heard a story that the man before bumped into her or made a bad comment), but I think what she did really is considered assault.
Now, towards the end, we see the man getting tackled. I think what happened is that when the police came, they saw him attacking her and assumed the worst and arrested him. The police probably didn't see the first part of the fight. And I do think the man was in the wrong when he attacked her when she walked away.
But, in my honest opinion, I do believe this fight 'started' when she grabbed his neck and was making punching gestures at him. In my book, that's assault.