Note here: a single blow from the hand constitutes ‘deadly force’ in point of fact, and reciprocal force is justified.
That old ‘sock on the jaw’ or ‘punch in the beezus’ from vintage films can kill you.
I remember watching westerns and crime dramas and old movies as a kid when the bad guys who were planning a robbery would resolve to "knock out the guards" so as to not get the death penalty if they were caught. I'm sure I was not alone in thinking that hitting a guy on the head with a gun would merely knock him out and not kill him.
The victim in this case seems to have died from hitting his head on the floor rather than from the blow itself.