it looks like he knew the guy and had a long running feud with him. Saw him at the gas station and walked right up and punched him in the face - but this time it was a perfect storm - as the punched guy fell, he hit his head on concrete ... so, not really a one punch kill more like an unlucky fall .
unfortunately most states will not let you shoot to avoid a fistfight.
I am sort of lucky in that NV grants special protections to "older people" if you attack an older person they can levy more charges, also - I had knee surgery ( ACL replacement ) and I cannot run away .
IMO one should be able to shoot an unarmed assailant - if you are an innocent bystander/jogger/dog walker - it should not be ok for random jerk to walk up and start punching you, but I do not rule the world - it is best to be very familiar with self defense laws where you live