Bucking with a rider in the saddle is a dangerous habit that needs to be resolved. By nature, some horses naturally do tend to buck more than others.

Many young, unhandled horses buck as a natural initial response to a saddle and rider on their back. If ground training is appropriate though, there should be minimal bucking with a rider up. If the right cues are given by the rider, most of the horses that do buck quickly abandon the behavior.

Horses are also taught to buck or continue to buck in the same way they are taught to engage in many other unwanted behaviors. They perceive the behavior to be easier and more rewarding than alternative (desirable) behaviors.

Like many evasive habits, bucking can also be a response to pain. A variety of physical problems may cause a horse to buck including mouth problems (loose wolf tooth, mouth wound, a snaffle that pinches the corner of the mouth), ill-fitting saddles, back pain, irritation under the saddle pad, or lameness due to an undiagnosed injury. A stimulus like a bee sting can cause a horse to uncharacteristically buck. Your vet can help you determine whether bucking is a result of physical pain.