How do you fix a horse that does not accept the leg in dressage?

A horse that does not accept the leg — swishing its tail, pinning its ears, tensing its back, or showing other resistance responses when the rider's leg is applied — is communicating discomfort or disagreement with the leg contact, and the nature of the response determines whether the correction is primarily training-based or requires addressing a physical or equipment issue first. Leg resistance that appears suddenly in a horse that previously accepted the leg readily should trigger an immediate check for physical causes: saddle pinching or causing pressure points, back soreness that makes the horse reactive to weight and leg contact, gastric ulcers that produce sensitivity to pressure on the belly, or skin irritation from boots or wraps. A horse that has always been somewhat resistant to the leg rather than showing a sudden change is more likely showing a training pattern that needs systematic correction. For training-based leg resistance, the correction distinguishes between the horse that is sensitive but evasive — resisting the leg because it does not want to work harder — and the horse that is oversensitized — reactive to the leg from excessive spur use or leg aids that have been applied too harshly. The oversensitized horse needs desensitization to the leg contact: systematic work in which the leg is applied very lightly and gradually, with immediate release the moment the horse softens and accepts rather than resists, and without escalating to spur or whip until the horse is genuinely calm about the basic leg contact. The evasive horse needs the clear, immediate escalation from light leg to a more definitive aid when the light leg is ignored, with complete release the moment forward movement is produced. In both cases, the leg should never be maintained through resistance without producing a response — sustained leg against a resisting horse reinforces the resistance rather than resolving it.