system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How does getting hit in the face (such as during a fight) knock someone unconscious?

I want to know how :
1. The body reacts, causing it to go unconscious.
2. How the body thinks going limp is a good idea when in a fight.

Thanks!
gpt
To answer your 2nd question first, it has nothing to do with your body's idea of what is good, any more than your computer getting rebooted by a brief power flicker of your house is a good idea of your computer's.

Most doctors believe a knockout is typically caused by the brain bouncing around in the inside of the skull. It doesn’t necessarily have to be one really hard hit, but a series of hits that continuously cause your head to snap in all different directions with your brain rattling in the inside of your skull like a shake weight. 

 Imagine that soft, mushy brain smacking against the inside of your cranium and those thin connective tissues holding it being stretched and torn; that is what causes your brain to shutdown.

When fighters get knocked out by a series of strikes in a fight, it’s not uncommon that they describe sensations of disorientation: blurred vision, lack of foot coordination, disrupted balance, numbness, etc. As they continue getting hit, these sensations intensify until the knockout hit is delivered and they finally lose consciousness.  Once out, our brains go through a "reboot" process that then leads to waking back up from a knockout.

A knockout strike has more to do with how the skull rotates in response to the strike rather than the power behind it.  Arguably, the most vulnerable point to hit someone and achieve a knockout is the chin and jaw area.  The reason is simple anatomy: The chin is a knockout button because it’s a leverage point that causes the most head movement when hit hard enough. A good whack on the chin causes the bobble-head effect more so than a strike on any other area on the head/face.  Side strikes, especially to the temple and back of the jaw areas are close runner ups.