This tells you it's a circus. There is ZERO standard deviation between UoF as a civilian than a LEO. I'm certified to teach BOTH now. If you are reasonably certain that grievous bodily hard is the outcome, you can use deadly force to defend yourself. Even 'civilians' can defend others, the standard is the damage the aggressor is capable of doing.
There is a standard to not engage as a civilian, which is fine. But Kyle didn't engage, he fled. While fleeing the area, he was under continual attack by both disproportional numbers, size, 'Lefty' had a gun, and one case a weapon of opportunity (skateboard). Both are articulable facts that allow disparate force.
I've said it before, if he were my kid, I'd have gone and bought a leather belt. But he's not the one at fault for this situation.