This situation presents a snap-shot of our modern times. The violence in our world and the lack of accountability for ones actions makes "starting some----" easier. Those three girls were approaching this couple with a gang mentality. One on one with no audience it probably would have never happened.
The reason that the guy didn't react well to these attackers is that it is very difficult to split ones focus on three attackers and the protection of your girl friend. Also no matter how big and nasty these women attackers were it comes down to this,if the guy hauls off and hits the women society paints him as the bad guy.
Where are the police you ask? It's too much to ask that the police be front and center at the scene of every dustup on the streets. Most of their job is follow-up to crimes already commited.
I'm not trying to paint the boy friend out as a wimp, but I am old enough to remember when standing up for the women in that situation would've been a given. Courage and a cool head under pressure are makes one a man instead of a sheep.

just some thoughts, Mark