This is going to be a tough call. Usually you can only use deadly force to protect your life (or others) from threat of death or serious bodily harm. If the threat retreats then the justification for deadly force may also be void, even if the threat got in a punch. You also have to have clean hands yourself. It would have been better it seems if he had just recovered and filed assault charges. Better still if he hadn't harassed the family member over parking, if in fact he did that. At this point his only defense might be that he was disoriented from the assault and still felt threatened with further assault (passion of the moment plea).
He didn’t harass anyone over “parking”. He informed the woman that she was parked illegally, which any law abiding Citizen should have done. Also notice that the attacker was advancing to continue the violent assault until the moment he saw the gun being drawn.
Bingo!
That is the entire case for the Defense. It sounds like reasonable grounds for the self-defense claim to me - but I am not on the jury.
Anyone who expresses a similar belief is not going to be on the jury either.