Snapping the Head
If you watch a fight you'll notice that nine times out of ten when someone gets knocked out it's right after the fighter's head got snapped around somehow. Whether it was a solid hook to the jaw, a spinning kick that landed behind the ear, or even an uppercut that rocked the recipient back on his heels, the important thing is the motion of the head. That sudden, forceful snap is actually what results in the knockout.
The Mechanics of The Knockout
While it's a little gross to think about, the human brain is actually floating in the jar of liquid that is the skull. When the head gets snapped around it make the brain jar against the skull, and that can result in disorientation, confusion, and a stuttering in the brain function. That momentary interruption is all it takes to send an opponent crashing to the floor, and the impact of the head on the ground is usually enough to finish what the original knockout punch began.
How Do I Do That?
It sounds easy, but if a one-punch K.O. was so simple then combat sports wouldn't be nearly so interesting. The goal is to land a forceful blow to the side of the head, and to spin it around. Ideal methods are a hook punch to the temple or to the jaw because those will hurt, disorient, and result in the snapping motion you want. A spinning kick delivers more force, but will be harder to aim.
For those who prefer the uppercut method, all you have to do is land a solid punch or palm-heel strike on the underside of the jaw, slamming up and rocking the head back. This will give you the right head motion, and it has the added benefit of compressing the nerves at the back of the neck for further pain and fight-ending potential.
Regardless of the particular blow someone uses it's important to execute proper technique. This means you don't punch with your arm, or kick with your leg; put your whole body behind the blow. Twist the hips, and direct the full force of your body so that it lands in a single, hard blow that will rattle your opponent's brain and end the fight in a single, decisive strike.
Is That The Only Way to Knock Someone Out?
Of course not. Rattling the brain is one of three ways to knock out an opponent. The other two methods are interrupting blood flow to the brain, or interrupting air flow. So if you strike the arteries in the neck hard enough to stutter the supply of blood, or if you hit someone so hard that he or she can't breathe then it's very likely they'll pass out. When it comes to blood and air interruption it's a much safer option to implement submission holds rather than to try and strike key areas. Holds like The Guillotine or the infamous Sleeper Hold are perhaps two of the most well-known blood chokes used in MMA today.