Can a fart really knock someone unconscious

There are three main ways.

1. You cut off the oxygen/blood-flow to the brain via a sleeper-hold or some other choke. About ten seconds of a proper choke can render someone unconscious, and twenty seconds can cause brain damage or death.

2. You hit them hard in the head and cause their brain to rock back and forth within their skull. In doing so the brain is put at serious risk of bruising. To solve this problem, the body has a natural defence system - the person falls unconscious, allowing their body to become horizontal and stable, thus restabilizing the brain to keep it safe from bruising and damage. To knock someone out this way, a powerful blow to the back of the head will work best, although side or frontal-blows to the skull can also be effective, just harder to do properly.

3. You cause their head to turn to one side very quickly and forcefully, putting pressure on the spinal cord. This overloads the spinal cord with nerve signals and impulses and puts the body into self-defence mode in which the person loses consciousness and falls down, allowing the body to restabilize. This is the most common knockout in boxing and Muay Thai. A well-aimed, powerful hook to the opponent's jaw will cause their head to turn sharply, causing this sort of knockout.

In a self-defence situation, a sleeper-hold executed from a BJJ-style rear guard position will work; or a nice, powerful hook-punch to the jaw. When attacked it's a bit hard to hit someone in the back of the head.