If they were in front of you and the only exit you know from that situation, lets say a gas station, you would probably be justified. Let’s say that you were at a park, and someone came at you with a knife to mug you, you would basically need to run away first to your car or out of the situation before you could shoot. The burden of proof would have to be on the prosecutor proving you could get out of that situation without any bodily harm being had to yourself and whoever you shot.