You may remember hearing tasers, beanbag rounds, pepper spray, and other such weapons as nonlethal. This was a lie to hide from an inconvenient truth: Human bodies are extremely good at compensating for serious injury or illness. These things have since been rebranded as "less lethal", which is definitely better, but we still regularly hide the true risk of using such weaponry.
It's very hard to create something that can do enough damage to stop a person without also doing enough damage to kill them. Add in the requirement that damage be reversible and it becomes nearly impossible. Tasers aren't nearly as safe as claimed.
The humane way to deal with a combative person is to give them space and keep others out of harm's way. This reduces risk to everyone involved. People get tired and stop fighting after a while, no matter what made them so upset in the first place. Obviously, every situation is different and sometimes direct intervention is required, but not the way the USA does it.. not at all.
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Ever heard of the dude who got a railroad spike shoved into his head and didn't notice? He lived for a while not knowing about it, eventually a doctor pulled it out, he survived that and kept on living. Unfortunately, the brain damage radically altered his personality for the worse, but the point is an example of how human bodies survive things really well, sometimes without you even being aware.
Another example involves someone who was shot in the head. Their friend was also shot in the head and died, but it was hard to treat the first person because they didn't understand that they were injured and were so focused on trying to get their friend help that they couldn't even see that the other person was dead.
These stories are fairly rare, because usually lethal damage is .. lethal. But the point is that the line between lethal and incapacitated is thin.
(Oh yea, and you know how movies always portray getting knocked out as no big deal? That's just not true. Anything that does enough to you to make you unconscious is going to have permanent damage with rare exception.)