Why does my reining horse overreact to my leg?

A reining horse that overreacts to the leg — shooting forward, spinning suddenly, or making dramatic movements in response to a small or inadvertent leg contact — is either extremely sensitive by nature and training, or has been trained to respond to a very light leg through the cue-and-release process that makes reining horses light. In either case, the overreaction from the beginner rider's perspective is often simply accurate response from the horse's perspective: the horse felt a leg contact and responded correctly to what it was trained to respond to, while the beginner did not intend to apply a leg at all. A beginning rider with developing position produces inadvertent leg movement constantly — gripping with the lower leg, bracing against the stirrup, losing balance and catching it with the leg — and a sensitive, well-trained horse responds to all of those contacts as if they were deliberate aids. The solution is developing positional stability that reduces the inadvertent leg movement: exercises without stirrups build the hip and thigh stability that allows the lower leg to hang quietly rather than actively gripping and shifting; balance work at slower speeds builds the security that reduces the reflexive leg grabbing that balance recovery produces. Until the position is stable enough to keep the leg quiet consistently, a horse less sensitive to inadvertent leg contact is a more appropriate learning partner than a highly sensitive reining horse. The experience of riding a horse that responds accurately to unintentional aids is valuable information about what the rider's body is actually communicating, but it is difficult to use that information productively for improvement if the responses are dramatic or unsafe.