In my state, you may use deadly force if at the time of its use, you held a good faith belief based on objective facts, that you were in imminent fear [danger] of serious bodily harm [or worse]. The threat does not have to be real, only that you believed it to be so. There are a few exceptions like those mentioned above. For example, you must have a legal right to be where you are. If you are party to the confrontation/escalation, you must retreat until you can no long do so safely while telling your assailant that you do not wish to fight.. to leave you alone. When you can no longer retreat safely, you regain the veil of innocence and may use deadly force if necessary.