Call the police. There's no excuse for that type of crap.
If it was me he'd of had a broke nose after the second swing, but you were probably smart for staying out of it at the time. Some of the most dangerous situations you can get into are domestic disputes, as you can't tell how EITHER party is going to react when you intervene.
It won't end until someone confronts the kid. If she's making excuses for him, the little prick has got her under control and she'll lie like crazy to protect him...
