Although .... When I lived in London I stopped a guy from beating up his girlfriend (he was, simply put beating her along the street). I had the girlfriend start attacking me with her stiletto
A friend in Amsterdam stopped a guy in the process of beating a woman on the street. He had to disable the guy (with a strike) to get him to stop. The woman promptly attacked my friend.
I think it's very common in domestic violence situations for the receiver to defend the aggressor.