My horse started rearing when we stop and it is scary what can I do to fix it?

Rearing is the most dangerous behavior a horse under saddle can develop, and it needs to be stated clearly at the outset — a horse that rears while being ridden is a horse that can kill or seriously injure his rider, and the danger is not proportional to the height of the rear. Even a small rear can go wrong catastrophically if the horse loses his balance, the rider is caught off guard, or the horse develops the habit of going higher as the behavior escalates. Take this seriously from the first instance, not after it becomes established, and do not minimize it because it only happened once or twice or because the rears are currently small. Rearing almost always gets worse before it gets better if not addressed correctly and promptly. Before anything else, get off and call your veterinarian. A horse that suddenly starts rearing when asked to stop is frequently a horse in pain — back soreness, hock pain, kissing spine, ulcers, and sharp dental points that cause bit pain during downward transitions are all documented physical causes of rearing behavior. Something changed physically, and finding that cause is not just important for fixing the behavior — it is important for the horse's welfare. Tack evaluation runs parallel to the veterinary check. A saddle that pinches or bridges when the horse rounds his back during a stop creates pain at exactly the moment the behavior occurs. A bit that is too severe, incorrectly fitted, or used with hands that are too strong during the downward transition creates mouth pain that the horse attempts to escape by going up. The one-rein emergency response is critical to have before you ride this horse again. If a horse begins to rear, immediately bend his head to one side with one rein — do not pull straight back with both reins. Pulling straight back with two hands when a horse is going up has no mechanical advantage and can actually encourage the horse to go higher. Bending the head to one side disrupts the horse's balance and forces him to think about his feet rather than continuing upward. Do not school this horse through rearing alone if the behavior is occurring under saddle. Get professional help now, before the rears get higher, before a fall happens, and before the habit becomes deeply established. Rearing is one of the few behaviors where getting the response slightly wrong can make the situation significantly more dangerous, and that is not a margin for error anyone should be navigating without experienced guidance.