A single punch isn’t likely to be legally construed as deadly force, allowing deadly self defense. It certainly is sufficient provocation to change murder to manslaughter.
How does anyone know what’s in the mind of the attacker? One punch is indicative of a willingness to assault and who knows how far the attacker intends to take it? Should the victim wait until he’s seriously injured before fighting back? If I were on the jury it would be an immediate not guilty.
I can kill you with one punch.
Depends on the state. Fear of “serious bodily harm,” is grounds for lethal response in some states.
As long as the shots were not in his back.
He kept coming at me. His punch in my head made it difficult to think..
Tell ya what.
You let this guy punch you in the face and then tell me how it's not deadly force.
Oh wait. You won't be able to. You'll be dead.
Samoans are well-known for being able to kill with one punch.

Single punch can kill. And more can kill if the victim has a hidden health weakness problem.
First, Knockout Game was covered fully by the late Colin Flaherty in books and videos such as White Girl Bleed A Lot.
Also, some others:
One-punch killings: They happen more often than you ...
Oregon Live
oregonlive.com Jul 20, 2015 — Lewis Allen Wilson apparently was the victim of a bar fight that spun out of control, and he died from a blow to the head. No suspect was ....
The man who killed a stranger with a single punch.
in The Guardian , May 14, 2022 — Jacob Dunne spent his life dealing drugs and getting into fights until, in 2011, he struck a deadly blow.
One Punch Can Kill – Unlawful Striking Causing Death
Corney & Lind Lawyers
corneyandlind.com.au (Australia)
Queensland’s Safe Night Out Act 2014 endorses harsher penalties under the Criminal Code for a ‘one punch can kill’ scenario.
One Punch Assaults Causing Death
www.gotocourt.com.au ›
After to several highly-publicised one punch assaults....
I disagree. People are killed by a single punch.
Either the punch in and of itself, or falling back and hitting our heads.
If I am on that jury the shooter walks. And I am not a trigger happy person.
Above is the first article after a search with “elderly man killed with one punch”. (Many people would consider me “elderly”) But even young people can be killed with one punch.
The search came back with 94 million responses.