It doesn’t matter if she taunted the police or not. He wronged her. His behavior is caught on video and substantiated.
There is no “but”. You are trying to weakly justify his behavior.
“He shouldn’t have hit her.” Period. He is responsible for his behavior, not her behavior.
At first I was with you on this but a closer look shows that she was taunting the police, trying to get their attention or anger them in some way to overreact toward her. Start there and then place blame for the punch/slap if you must but don't start with a lie.