The distinction between passing out and knocking out is very simple:
1) Passing Out: Your body is so tired that it can’t go on.
2) Knocking Out: Someone else is traumatically forcing your brain to rapidly shut itself off by convincing it that its dying.
When you’re talking about hitting someone in the head as opposed to strangulation, this generally means a concussion. They have hit your head so hard your brain has bruised itself against the inside of your skull and you have now gone unconscious. When you punch someone in the head, you have zero control over what actually happens to them. You can hope, but you can’t control it. In comparison to a choke hold, where you have almost total control over their body and can feel for the moment they go limp (and a mistake is still going to potentially end their life), it isn’t worth it as a tactical choice.
Humans are persistence predators, they can go and go and go for a very long time. You have to work pretty hard to physically exhaust them to the point where they’ll collapse on the battlefield. Their brain/body will usually stop them long before that point arrives. When you’re talking about combat, they’re far more likely to die before they ever reach a point of total exhaustion. We’re talking days without rest, the kind you’re only ever likely to encounter in mass battles or with a character who is being hunted.
The truth is that if you see a character who has been consistently knocked out multiple times on screen, they’d either be suffering from serious damage to their brains or dead. Most of them would be dead. If you ever feel like testing the theory out, go check out the late life prospects for boxers and football players who’ve sustained several concussions over the course of their careers.
The whole “knock someone out to get rid of them” is a Hollywood trope built for narrative convenience. The actual process of physically subduing someone is long, drawn out, and takes a great deal more energy and effort than a one, two punch or a knife to the gut.
The “Knocking Out” Contrivance in media acts like character death but without the audience having to evaluate the protagonist’s morals or the narrative’s values. They maintain their “good guy” street cred, and the audience doesn’t have to ask the questions. We switch easily from one scene to the next without any of the hoopla. The audience gets their action sequence and no one needs to feel bad. It’s a bloodless death. Or it’s a scene transition, or someone’s been taken prisoner without the author having to figure out how they move tie them up, move them, and get them from Point A to Point B. (Nevermind that it’s actually much harder to move dead weight than it is someone who is conscious.)
No, yeah, it is.
It’s there for shock value when the protagonist is taken prisoner.
Still, if you want to use this narrative contrivance in your story you can. No one will stop you. The vast majority of general audiences won’t question it. Judging by the number of questions we’ve received about this topic alone, people do commonly think the knockout genuinely works as a tactic for subduing the enemy. However…
The “Knockout” is prevalent in media because it is a convenient narrative tool.
If you’ve got a burning need to use it then use it, just don’t sit there and try to say it’s “realistic” or safe after the fact. It isn’t. Accept the narrative knockout for the bit of smoke and mirrors it is, and move forward.
It’s part of a collection of tropes that I like to call “Feel Good Violence”. They have no relationship to reality or responsibility, but they’ll make the audience feel good and the character seem powerful. It is “Feel Good”.
So, that’s it. I have nothing more to say that we haven’t covered in previous posts about head injuries. Unless @scriptmedic has anything they’d like to add, we’re done with the topic for now.