Falling was a type of self-defense move that allowed a person to land on the ground without causing a harmful impact to oneself.
In 2266, James T. Kirk gave Charles Evans a lesson in proper falling techniques in the ship's gymnasium as preparation in learning how to fight. According to Kirk, the trick was that "you've got to slap the floor to absorb the energy when you fall."
After that lesson, Kirk decided to move on to the more advanced shoulder roll technique, however, after observing it, Evans declined, and Kirk ended the lesson. Evans promptly protested and Kirk explained that "you have to learn to protect yourself in a fall first. It's more than teaching you to defend yourself." (TOS: "Charlie X")