they get to beat on you. That is 100 percent self defense, with justifiable force, and he didn't continue to beat on her or anything like that. Not that it matters but If he wouldn't have punched her she looked like she was going to continue swinging. Gender has to be thrown out in a court of law. A human got attacked by another human, defended himself against said human, and didn't keep at it once the threat was eliminated. Also he tried to defuse the situation when she had made a fist and he tried to grab her arm and reason with her.

You don't even have to let someone be within arm's reach of you acting in a menacing manner, that's already assault. You just have to make sure you respond with appropriate and not excessive force.

Of course in the real world where people are biased idiots, he may be screwed.