ironic much?
That's not irony. That word is so frequently misused.
Anyway, the police don't get to slap people who bit them. This was a very poor attempt at custody and control from the get-go, so I'd fail the officers on that to start. Not a crime, but very poor policing.
I was unimpressed, but still with the officers until the hand comes up to strike after she's halfway down in the corner. That's anger. Anger at a situation that the officer, the man who is expected to know better, allowed to get out of control.
If two strapping lads can't take a woman sitting in a chair into custody without significant injury, they're no good as officers. If they raise a hand to strike in anger, they're common thugs who have reduced themselves to criminal acts.
Pushing her over the chair was the icing. That's spectacular incompetence.