So if I see you punch my wife, I can react by putting a bullet through your head? Is that what you're saying?
The cop's reaction was a wild and unjustified over-reaction. He needs to be fired before he over-reacts in a way which kills somebody.
> So if I see you punch my wife, I can react by putting a
> bullet through your head?
Actually, yes, on that question. A punch can be, and often is, “lethal level” force.
Variables to this would include how quickly you shot the attacker after the punch, the severity of the punch, from your wife’s point of view—not the punchers, whether it was in context of an argument or a random attack, and importantly (in this case), if your wife had provoked the punch by attacking first, etc.
According to the FBI (which confuses things a bit by combining the statistics), “Fists and feet were responsible for 745 murders in 2010, or 5.7 percent of all murders that year.”
So yes, under many circumstances it would be appropriate to shoot someone who had punched your wife. That you shot them in the head doesn’t really matter, except on an emotional level.