Like others have said, go through steps, not only to try to avoid a physical assault, but to satisfy legal requirements. Try to get away. If you can't, warn him verbally to stop. Draw your weapon, but don't point it at him, and tell him to stop. If he keeps coming, point it at him. You get the picture. In other words, if it comes down to legal prosecution, it should appear that you did absolutely EVERYTHING humanly possible to avoid escalation, step by step.
Beyond that, of course as always, it depends on the situation, your firearm, the state you live in, and your ability to shoot instinctively with speed and accuracy. In the situation described, I personally, if my back were to the wall, would take out his knee with a .357 158 gr. hollow point. If he didn't appear to be a hard criminal, just some jerk who drank too much, I'd shoot his foot. That may or may not work for you, again depending. The important thing is that you're seriously examining the concept and thinking about what you're doing, and not just blundering around like some armchair Rambo wannabe. You're doing fine.
Beyond that, of course as always, it depends on the situation, your firearm, the state you live in, and your ability to shoot instinctively with speed and accuracy. In the situation described, I personally, if my back were to the wall, would take out his knee with a .357 158 gr. hollow point. If he didn't appear to be a hard criminal, just some jerk who drank too much, I'd shoot his foot. That may or may not work for you, again depending. The important thing is that you're seriously examining the concept and thinking about what you're doing, and not just blundering around like some armchair Rambo wannabe. You're doing fine.