Stomping on an unarmed woman who had already been assaulted and thrown to the ground is "perhaps" excessive?
I have to interject here. It is clear from the video that he placed his foot on her shoulder, and then it slipped down on to her head when the friction of the sweatshirt against her undershirt gave way. Anyone familiar with walking in the woods knows the force your foot exerts downwards when it slipps off of a log or a rock. He wasn't intensionally "stomping" on her head.
Now, was there any reason for him to put his foot on her shoulder to begin with? No, especially when someone else was already holding her down and people were calling for the cops. The guy will probably be given a small fine and provide a public apology, but that's as far as that will go. As far as the gal, she will probably have to make a written apology for her actions, but that's it.
