Absolutely always wrong in any situation. If he's beating you down to point you think he may kill you, you at the attacker, the center of the target, not try a trick shot at a moving limb. If you're NOT in fear for you life or greivous bodily harm, you don't shoot at all.
Shooting at center mass with the intent to stop the attacker as quickly and surely as possible may be self defense. Trying to wound someone is aggravated mayhem.
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