Haven't I heard from some experienced LE folks that domestic disturbances are among the most dangerous calls an officer responds to? If the guys with bat belts, back-up, and cuffs think it's dangerous, how well are you going to fare with a raised voice and a knife that you may or may not be trained to use?
I think you can make a good argument one way or the other about opening the door to let the asshole know someone is actually paying attention and the cops are on their way. Once he took a punch, closed the door, and then decided to open it again to follow them, that's where it gets less defensible IMO.