A polo pony is actually any horse physically sound (not blind) and free of vice and under control. Reference to pony may come from pony size mounts used in the far east during the origins of the game, or it may be just a pet name more appropriate than 'baby' or 'sweetie'. The most popular mounts are half thoroughbred for speed and endurance, and half quarter horse for quickness and strength. Most commonly about 15-16 hands (60-64 inches at the withers or sholder) and weighing in at 1000 to 1500 pounds they certainly don't conjure the image of a pony.
The polo pony makes polo stand above all other sports. No other sport demands the skills and diverse performance from a horse, car, bike, or other vehicle integrated into a game situation. Most vehicles used in sports are fine tuned with percision performance characteristics, we also demand these from our mounts but must always keep in mind they have moods, attitudes, habits and an astounding ability to learn.
The rules of the game are designed for the mounts protection and respect. Notice Rule 21(f) call for an immediate stop of the game when a mount falls, but Rule 21(e) will stop the game for a fallen player only after the ball has entered neutral territory.
A player may be a powerful hitter with uncanney hand-eye coordination, but if he can't ride, he's worthless, a liability to any team. No one can deny the advice that a player should consider developing years of riding skills be for considering an enjoyable and safe polo game.
A chukka is only 7 minutes on the game clock but this is an eternity for a mount out of shape, or played abusively. Management of your mounts resources, both physical and mental, are as much a part of the game as knowing which direction your team is going.