Well, the punch served sure as hell it's purpose. He didn't have any more problems out of her. Although, a tasering would have been much more entertaining. I don't know if the officer had pepper spray or a taser with him.
Anyway, I'd say it's justified if a crowd of people are gathering and starting to interfere with a lone officer trying to make an arrest. I don't know what people think the officer should have done in this situation. I think I'd prefer to take a punch instead of a taser, pepper spray or metal asp strikes to the joints.