A bystander that intervenes in a purse snatching is one thing! A by stander that intervenes in a purse snatching by pulling a weapon and starts popping off rounds to apprehend that purse snatcher is out of his mind!
Phil
The way I understand it anyone who does anything at all to avoid being robbed, beaten or murdered in your part of the world is wrong.
That said, a purse snatching is not a shooting offense and thus the brandishing of a weapon in such a case is a felony. However, the little old lady or the sweet young thing who is under attack could in some cases use a firearm for defense if they thought they were in serious danger. It is a case by case thing and one answer does not fit all cases.
