What is under-spinning in reining?

Under-spinning in reining occurs when the horse stops before completing the number of revolutions the pattern specifies, resulting in a penalty for the accuracy failure regardless of the spin quality up to that point. Like over-spinning, under-spinning specifically penalizes the precision of the maneuver rather than its execution quality — a horse that spins correctly for three revolutions and then stops one-quarter revolution short of a three-and-a-quarter count has performed the spin correctly but stopped it incorrectly. The under-spin penalty applies when the horse is one-quarter revolution or more short of the required count, and it affects the final score as a fixed deduction. Under-spinning is less common than over-spinning in most beginner competitors but occurs in specific situations: a horse that anticipates stopping and begins to slow or halt before the rider asks, a horse that is physically tired or sore partway through the spin and slows to a stop, or a rider who loses count and stops too early thinking the required number has been reached. For riders who tend to under-spin, practicing with a very deliberate and consistent count during training — and specifically practicing going past what feels like the natural stopping point by a small margin to build the habit of riding through the full count — corrects the tendency over time. Riders who are uncertain between over-spinning and under-spinning as their primary error should count revolutions during competition practice specifically, without worrying about other elements of the spin, until the count becomes automatic and can be managed simultaneously with the other riding demands the spin places on the rider's attention.