"unreasonable due to the great disparity in weight, height and strength." This is reaching, where in the paragraph does it take those into account?
He didn't beat her senselessly, he responded to the initial assault, then gave her a sort of bodily warning/gesture, she then proceeded to assault him this time slapping across the face, which he then responses to with a punch. This is perfectly reasonable and legal, he did not continue to pound her when she fell to the floor, he did not take out an weapon, he walked away after the incident. My only critic was that he didn't notify the authorities and file a police report.