Agreed. And having been blindsided by an unknown party with enough force to take you off your feet, and then having them upright standing over you; while you are now completely defenseless save for your gun; sounds like the perfect reason to shoot in self defense. Remember... there is no prior conversation between the victim, and the assailant. He has no way of knowing his intent, or motivations.
A guy came into the store and told the father something, which caused him to head out there..
I would never shoot a person for pushing me down, ever, and dont appreciate anyone owning deadly weapons that feels the opposite....Thats ******* insanity as a threshold. Also doing so without second thought and without seeing a weapon on the guy that pushed you..if you dont have your WITS about you you dont need to be carrying guns.