How do you fix a horse that is crooked on the centerline in dressage?

A horse that tracks crookedly on the centerline — haunches falling to one side rather than following directly behind the shoulders in a straight line from A to C — is showing a straightness problem that reflects the horse's natural crookedness and the training work needed to address it systematically. The centerline reveals crookedness more unmercifully than almost any other movement because there is no wall, track, or other physical boundary to hide behind — the horse must maintain its own straightness over the full length of the arena, and any tendency for the haunches to drift right or left becomes immediately visible to the judge at C. The correction for centerline crookedness begins not on the centerline itself but in all the work that precedes it: developing genuine straightness through systematic shoulder-fore, shoulder-in, and transitions that consistently address the horse's natural tendency to drift one direction. Most horses tend to drift their haunches toward the inside of the arena, which means the correction often involves using the outside leg more firmly to keep the haunches from drifting inward while the outside rein contains the shoulder from falling out. On the centerline specifically, riding slightly more to the haunches' falling side — positioning the shoulders fractionally toward the direction the haunches are drifting — corrects the visual impression by keeping the horse's tracks aligned even when some natural crookedness remains. The shoulder-fore position applied subtly on the centerline keeps the horse's inside shoulder slightly in front of the inside hind — preventing the haunches from leading — and is the most commonly used correction for centerline crookedness in competition. Halts on the centerline that are not square — the horse's hind legs not standing parallel and even — often reveal and result from the same straightness issue, and addressing the straightness improves both the track and the halt simultaneously.