A horse pulling during the downward transition is a common problem. Typically, in an effort to resist the rider’s hands, the horse disengages its hocks so that the hind legs can be used to brace against the rider’s hands. Then, the horse is able to flatten its back and neck and thrust its forehand weight onto the rider’s hands, allowing the horse to pull much harder than if it were pulling with the weight of its head alone.
To correct this problem, you have to start at the source–the horse’s haunches–by keeping your legs firmly against the horse’s side throughout the downward transition, making it impossible for the horse to disengage its hocks. Simultaneously, you need to perform numerous half-halts, which will prevent the horse from finding a fixed hand against which to pull.
If the horse continues to resist by throwing its hocks out behind its body and pulling when you ask for the downward transition, use your stick to punish the horse, tapping the animal on its barrel to reinforce your supporting leg. If necessary, increase the force with which you use the stick to the point that the horse keeps its hocks engaged and doesn’t pull against your hands.
Finally, be sure that you lighten the weight of your hands on the reins as the horse decreases its pulling, so that the animal will get a reward for the correct response. You should still keep your hands closed into fists, with your thumbs serving as stoppers to keep the reins from slipping through your hands; but your arms should be mobile, sensitively moving forward and back with the motion of the horse’s head, rather than staying fixed. This subtle mobility is the mark of “good hands.”