This goes back to primitive times when the ability to produce and raise children was the survival or failure of a community. Hitting females could induce miscarriages and so men learned very early they had to protect their mates, or the family group was doomed. We are talking life and death stuff here - damaging females is so dumb the message has to get through....
While I don't condone violence against anyone, men are generally stronger than women therefore it is just morally wrong to do so. Being a victim of this myself, it is not a very good feeling and i can say it is completely different than being hit by another woman,
Believe it or not, I'm pretty sure it was a guy. It's ridiculous though, in my opinion. Equal rights should mean equal treatment. Any reason that could be used for hitting a man should be just as applicable for hitting a woman.
When I was a kid my two older sisters pounded on me constantly, I was smaller and weaker, but I was not allowed to hit MY LITTLE sister, or any girl for any reason. Now, ANYONE who hits me, gets hit back.