A protip for disabling blows is that any weapon strike toward the head is intended to be lethal. Knocking someone out is causing them brain damage, it’s hitting them hard enough so that they’re brain goes “nope! I’m not working anymore!” and you can deliver more pinpoint directed force by driving a weapon sideways into someone’s head than you can by swinging it. The ends of most weapons in the middle ages like the pommel of a sword or the end of the shaft in a battle axe were designed so they could be used as weapons. Even the flat of a blade can be dangerous, though less so than the others. She’d either be hitting them in the cheek, the jaw, or the temple.
This opponent on the field of battle is also, more than likely, going to be wearing a helmet. So, even then, it’s not really going to work.
Frankly, unless there’s a specific reason not to kill this person then it’s best to just finish it. Either that or stab them so they can’t follow and pray. If you’re going to write characters that fight, especially characters who use weapons, it’s best to get used to the idea that they’re going to kill people.
Disabling doesn’t work like it does in the movies where a single blow to the head knocks someone out and it’s all good. It’s slightly more involved. Disabling blows will be striking the hands, the wrists, or the other joints like the knees and shoulders as a means of stopping the other person from hitting back. With the exposed body, you can also strike bone and muscle with a blunt weapon to stun it and make moving painful. Pain is a decent motivator (which doesn’t always work) to making someone else stop. The success tends to depend on the person who is on the receiving end. They’re the ones who actually decide how far the person trying to disable them has to push, and they can hurt themselves more than necessary by refusing to give in after they’ve been secured.
Unless you’re trying to actually kill your enemy, you don’t move to any of the serious vulnerable points. The key to understanding disabling as a fighting style is that the goal is to keep your opponent awake and conscious, you’re just starting on the outside of the body and working your way inward. This is going to be much more difficult if they’re in armor.
If you’ve hit someone hard enough in the head that they’ve blacked out, then you’re running the risk of them never waking up again. The risk of them actually dying goes through the roof if they’re unconscious for more than a few seconds. Again, this is brain damage. It isn’t “and then, sleep”. Even if they do manage to luck out, we get into other problems that aren’t solved with a knockout like what happens to them next. The other characters leaving them unconscious on the battlefield is under the assumption that they’ll be fine, but without any guarantee. There’s no guarantee no one else will kill them. No guarantee they’ll stay down long enough for the characters to get away.
If the character wants to disable this other character then they have to either damage them so they can’t fight back or chase them if they’re planning to run. If they’re planning to stick around, then they need to take them prisoner.
The easiest way to do this if the other person doesn’t see them coming may be to simply press the tip or edge of their blade against some exposed portion of the enemy’s throat while standing behind/beside them. Of course, if they’re side isn’t in control of the battle then they’re in a stalemate that has an out. If they’re not, then they’re in a stalemate that will probably lead to their eventual death or capture.
They can wound them or cripple, which will vary in difficulty. It does count as disabling and will be quicker than trying to do it without leaving a permanent injury. However, this won’t stop them from yelling or trying to attract attention from their friends. It also won’t stop them from screaming. It also doesn’t guarantee that they won’t die. Whether that death comes from blood loss, infection, or another less scrupulous warrior finishing them off after our heroes have gone on their way. Even if they are killed, they may not die immediately. Death can take awhile.
This is where I say that disabling or subduing someone else in a way that doesn’t harm them takes time. It takes a great deal more time and effort than simply killing them. It’s the kind of time a lot of characters just don’t have. A lot of violence is risk assessment and the weighing choices. Characters accept they can’t control everything, they’re in a race against time where they have to start making hard choices about what they need to do rather than what they’d prefer to do. They’re making decisions based on the information they have available.
Depending on the surrounding situation and their understanding of it, this character may be asked to choose between the life of their comrade and the life of the enemy who is kneeling/standing over them.
They can knock them over and take them prisoner, but if they have to run then they’ve got to run with them or leave them to tell their superiors where they’ve gone. If they’re friend is wounded, then they’re trying to save/carry their wounded friend while holding this prisoner hostage as they attempt to run.
In fiction, the knockout has become a sort of cheap way out so characters can avoid consequences or guilt over causing a death. None of this means you can’t do it, but it’s worth thinking about alternate avenues that are ultimately more interesting and put more stress on the characters in question. At it’s heart, violence in fiction is about consequences and how a character deals with them is a defining aspect of who they are. Your character could knock this guy out on the assumption that he’ll survive, only to learn later that he died.
How would they deal with that?
Some people might say it’s cheesy, but accidentally killing someone is real and it happens. Unintended consequences are a huge part of violence confrontations and are most often forgotten unless the writer is looking to teach the audience “a lesson”. However, it’s worthwhile to think about. Especially if you’re dealing with younger characters or those new to violence. Older/more experienced characters look for ways to mitigate them. There are answers to how they handle it which go beyond the breakdown or the angst-ridden cliches.
I’m not going to ask why this warrior is doing something as risky as stopping and kneeling if they’re still in the middle of a battle. That is a very exposed position. If they’re planning on actually killing them, they’ll stay on their feet as it’s more defensible and check their face (to see if they’re worth money) then cut their throat with the tip of their blade. You don’t need to be leaning over to do that. (And if that’s the case, the character probably won’t get to them in time.)
Otherwise the character is attacking someone… who may be friendly. Possibly might be, causing them brain damage is probably a bad idea.