Generally, given the experiences the girls I've dated have gone through they are far more capable of dealing with being attacked than most other people. However, on the flip side, being attacked has made them break down from what they've dealt with and the memories of it.
I'm known to step in and scare off anyone who goes after my gf, or friends in general. Woe to the person who attacks my loved ones in my presence. Someone threw a chair at my young friend, the one who's baby I watch every week about 4, 5 years ago while we were in school. I heard it from down the hall and heard her scream. I left my class and went after him. He tried hitting me with the same chair and I knocked it back into him and proceeded to run him out of the building attempting to club him with it. If I hadn't been so enraged as to think to drop the chair when running after him, I would have caught him and really hurt him. It's probably good I wasn't thinking clearly. I was about twice his size and 4 years older than him.
I've got a nasty temper and seeing someone hurt my friends and loved ones sets it off with a vengeance. One of my girlfriends dealt with a great deal of abuse and kept me away from her family because of it. The day I had to step in between my gf, her mother and her step-father was NASTY. She had to drag me from the house after the mother hit me and I nearly snapped and went to hit her back.
I have absolutely not gender stereotypes with who not to hit. I've been hit by boys and girls, and honestly, anyone with the nerve to physically strike me deserves the same response.
As far as the reverse, often my SO, or even friends, step in to defend me. I don't mind this, as I know why they do it. They know very well I can take care of myself. However, they also know my temper and step in to diffuse the situation and allow me to control it. My ex in my old avatar once put a knife into someones forearm for coming after me. Quite a bit extreme, but neither of us saw the person again.
However, there are times when what I see goes too far and I simply push my SO or friends out of the way and go after a person. The day one of my friends broke down next to me when sighting the guy who raped her while we were out was a bad day. She had to latch herself onto me to keep me from being arrested for going after him and beating him into the ground.
I've gotten into arguments with people who go after my loved ones that on occasion leave them crying and hysterical. Oddly enough, it's more often guys than girls. The girls have sense enough to avoid continuing it with me, unless we're dating of course.
Generally though, I'll allow whomever I'm with to look after themselves unless in knowing them, I know they aren't able to handle the situation well. My ex and her parents for example, if she didn't do what she was told she was hit, and if she faught back with her mother, the step-father joined in and she had no chance. I therefore stepped in to protect her. My friend, she's tiny and won't fight, her being struck by a chair set me off knowing this. She's afraid cleaning will kill bugs and she gets upset by that, why hit her? She won't fight back whatsoever and yet, when I had arrived he was attempting to hit her again. I didn't think the boy had enough nerve to try hitting me with that chair, but boy did he run afterwards.