He neutralizes a threat to his own life in a non-lethal manner. You know he could have done much more than given her a bloody nose. Considering the emotional struggle he's undergoing in that particular storyline, at that particular moment, that cop is lucky to have come out with just a bloody nose. That's restraint right there.
And, really, not a man for hitting a woman? That's patriarchal like no one's business. Saying that a woman is not a threat? That they deserve special treatment when they're cops and carrying a gun, eh?
Rooting for the bad guys...right, because punching someone in the nose and taking away a firearm is totally a good reason to support robbers, rapists, murderous lunatics, and the Joker.