Why does my horse walk forward in the spin?

A horse that walks forward in the spin — advancing or drifting ahead rather than turning in place around the inside hind foot — is not moving its shoulders correctly, lacks the balance to maintain the pivot position, is being pulled around by the reins in a way that drives forward momentum rather than rotation, or does not yet understand the specific body mechanics the spin requires. Each cause produces the same visible result but needs a different correction. A horse that does not move its shoulders independently — that turns by walking the front end around rather than crossing the inside front over the outside front — will consistently drift forward because the crossover motion is what creates rotation around the pivot rather than forward travel. Teaching the horse to move its shoulders specifically, through exercises like leg yields and lateral work that isolate shoulder movement, builds the body awareness the spin requires. A horse being pulled around the spin by the inside rein is being driven forward by that pulling motion: the rein tips the nose, the shoulder follows the nose, and the horse walks in the direction the nose is pulled rather than rotating around the hind end. The inside rein should open and guide rather than pull, with the outside rein controlling the pace and the degree of bend, and the rider's inside leg at the girth driving the rotation from behind. Balance and strength also matter: a horse that is not yet physically capable of anchoring its hind end while its front end moves quickly will walk forward as the path of least resistance. Slowing the turnaround down to a pace where the horse can maintain correct body position and rewarding the pivot foot response is always the correct starting point for fixing forward drift.