Is this right when a woman/man are fighting? Guy/Female opinion wanted.?

I don't believe in domestic violence by any means. Is it right for a woman to hit a man, and the woman get away with it? I have a friend who beats on her man, and one day he got tired of it and when she came at him - he smacked her. Not hard, but enough to get her attention. She called the cops and had him arrested. Even though she had hit him, she is the woman. Again, I don't believe in any domestic violence. I don't hit my guy and he don't hit me. Do you think in this case he was justified? Why or why not. My friend is shocked cause I sided with him on this one.