The use of lethal force against unarmed suspects is incorrectly seen as unjustified by “the average man,” perhaps because TV and movies have conditioned the public to a false ethos that forbids good guys to “use more force” than bad guys. It’s similar to the equally false ethos that says you’re supposed to let the other guy shoot at you first before returning fire.
American law has long understood the concept of Disparity of Force. It covers situations in which the ostensibly unarmed criminal’s attack on his victim – in this case, a police officer – is so likely to cause death or great bodily harm that this physical advantage becomes the equivalent of a deadly weapon. This in turn warrants the victim officer’s recourse to a per se deadly weapon, usually a service firearm.
Force of numbers is an element that creates lethal force ability on the part of those attacking the victim officer. More often than not, a male violently attacking a female can constitute Disparity of Force. While this would not necessarily hold true for a female heavyweight kickboxing champion fighting Casper Milquetoast, the courts understand that males generally have much greater upper body strength than even females their own height and weight, and that the average male is taller, heavier, and stronger than the average female of our species.
A great disparity in size and strength can also constitute Disparity of Force.
(When you testify for your officer in such a case, mention to the jury that this is why Heavyweights are forbidden to fight Flyweights in boxing matches and most other forms of “sport-fighting.”) An adult violently attacking a child is certainly another category of Disparity of Force, which a police officer might find need to apply in a rescue situation. Extremely high skill in unarmed fighting is another well-established example of Disparity of Force, but the officer will have to be able to articulate that he either knew that the man he or she shot was a black belt, professional fighter, etc., or show that such skill was obviously inferable from the opponent’s actions. For example, the officer has just seen the suspect sidekick two brother cops through a plate glass window.