Do you want to hear about the fact that the woman had an arrest warrant at some previous time, but not that day?Does the video begin at the first encounter?
Would arresting her without any outstanding warrants or suspicion of a recent crime be sufficient provocation to justify punching her in the face?
If you're waiting for the part where she made any move against him, you're going to be waiting a long time...unless informing an officer of the facts of the situation is now equal to battery and must be met subdued with immediate violence, fear for the officer's life, etc.
(I wouldn't be surprised.)