In a real life scenario, where I am witnessing, a mugging/assault such as you describe, I would draw my gun, whether or not I could see that the perpetrator was armed. I would make sure that my wife, and any innocents were out of the line of fire, while ordering him to stop his attack. If he stopped, I would continue to hold my gun on him while ordering him to the ground. He may or may not, comply, but I would continue to repeat my orders. I would hope that someone by this time had called 9-1-1. If I then noticed he was armed, I would tell him to keep his hands away from his gun. If he made any moves either towards me, or began to draw his weapon, I would shoot. The attacker, has already demonstrated, his willingness, to harm others, and is obviously able to overpower them, physically, so I would believe that my actions would be justified, as well as having witnesses, who could corroborate my version of events. JMHO