If person A attacks person B and B can't defend himself can you legally shoot A or only if you are doing it in your own self-defense?

Shooting anyone is bodily harm and possession with a weapon if you don't kill them. If you kill them you will go to prison for either manslaughter or 2nd degree murder. It's not worth it. One person attacking another person without a reason is an offence and you can press charges against them. I'd go with the law as weak as it can be. This person isn't worth going to prison for.

Actually, under the law in America, if you are justified in shooting an attacker in self defense you are justified to defend another INNOCENT victim just as if you were defending yourself. The catch is if the person you're defending turns out not to be an innocent victim you could face criminal charges.