In barrel racing, the contestant and her horse enter the arena at full speed. As they start the pattern, the horse and rider trigger an electronic eye that starts the clock. Then the racer rides a cloverleaf pattern around three barrels positioned in the arena, and sprints back out of the arena, tripping the eye and stopping the clock as she leaves. The contestant can touch or even move the barrels, but receives a five-second penalty for each barrel that is overturned. With the margin of victory measured in hundredths of seconds, knocking over one barrel spells disaster.