How do I stop a horse from rearing?

Rearing is one of the most dangerous behaviors a horse can exhibit under saddle because it risks flipping over backward onto the rider, and any training approach to it must prioritize safety above everything else. A horse that rears is not a project for an inexperienced rider — if you are not confident and experienced enough to stay centered and ride forward through the beginning of a rear, the horse should be in the hands of a professional trainer until the behavior is resolved. The immediate response to a rear is always forward: release rein pressure completely, lean forward over the horse's neck, and drive with both legs to send the horse forward the moment its front feet return to the ground. Pulling back on the reins during a rear is the most dangerous possible response — it can cause the horse to lose its balance and flip. Rearing almost always has an underlying cause: too much hand with not enough leg producing a horse that has nowhere to go but up; pain in the mouth, poll, or back; a horse that has learned rearing stops or avoids a demand; or a horse that is genuinely overwhelmed and fleeing vertically. Each of these causes requires a different response beyond the immediate ride-forward correction. A horse rearing from hand pressure needs a rider who develops a lighter, more following contact. A horse rearing from pain needs veterinary evaluation. A horse that has learned rearing works needs systematic retraining by an experienced hand that removes the reinforcement the behavior has been producing.