It comes down to the conditions set by a prosecutor as to reasonable defense compared to the adversary and situation. Outnumbered is one thing, one on one is another and the shift from defender to agressor depends generally on who escalates first and to what degree. *1 has fists #2 gets sucker punched and pulls a gun. #2 has ecalated the situation dramatically. Right and wrong start to fade away and the more prominent arguement becomes justified or not. That then is determined by a reasonable jury based on the arguements posed by the attourneys.
I am not a legal expert nor did I sleep in a Holiday Inn Express last night.