In Pennsylvania, we have two separate and distinct issues when it comes to use of deadly force outside of your house. First, is the standard use of deadly force (lethal force) under Pennsylvania law. To be justified (allowed), one may only use deadly or lethal force if you reasonably believe under the totality of the circumstances that you are in imminent fear of death, serious bodily injury, kidnapping or sexual assault.
The most heavily questioned element of self-defense cases typically surrounds the judgment call area: namely, is your use of lethal force reasonable? The reasonableness is judged objectively meaning would someone sitting in your skin knowing what you knew at the time (not judged later on knowing everything or with the benefit of cool-headed hindsight). While what you say can go into this calculation, simply saying “I was afraid for my life” is not an automatic pass. The jury is the one who takes a look at all of the information and determines ultimately not whether or not they would have done the same thing, but whether or not the government can disprove beyond a reasonable doubt that you acted reasonably under the circumstances to the situation that you found yourself in with the information that you knew at the time. It is the government’s burden to prove you were utterly unreasonable beyond a reasonable doubt.
The second aspect we need to be aware of is the notion of Stand Your Ground. In Pennsylvania, when outside of the house, one has a generalized duty to retreat before using lethal and deadly force BUT ONLY IF YOU CAN DO SO TO COMPLETE SAFETY. You do not have a duty to retreat if you cannot escape to total safety. For example, if there is a confrontation when the bad guy is on foot and you are in your car and he has a brick, then you have a duty to retreat (drive off) before using lethal deadly force. However, if you cannot drive off (such as because you are totally boxed in) or retreat with the ability to get to total and complete safety then you do not have to retreat before using lethal force.
Now we turn to Stand Your Ground in PA. If you did not start the situation and have “clean hands” and are in public in PA with a lawful deadly weapon and are in a place where you are allowed to be and not violating the law and the bad guy displays a weapon capable of causing death or serious bodily injury (such as a knife), you can stand your ground and use lethal, deadly force with no duty to retreat.
These two guidelines govern the question of: “When can I shoot someone when I am outside of the house?”