What causes a horse to depart on the wrong lead after a rollback?

A wrong-lead departure out of the rollback is one of the most common and most costly errors in a reining run, and it originates in one or more of the elements that precede the departure: crookedness through the stop or turn, poor hip position at the moment of departure, mistimed or unclear rider aids, insufficient preparation in the turn before the departure is asked, or physical discomfort that causes the horse to avoid loading the correct hind leg for the departure. Crookedness through the stop places the horse's body in an alignment that naturally sets up the wrong lead — a horse that stops with its hindquarters pushed left has its left hind loaded as the natural push-off leg, which produces a right-lead departure from a left rollback and vice versa. Correcting straightness in the stop corrects the alignment that the departure depends on. Poor hip position at the departure moment is closely related: if the horse's hindquarters drift to the outside of the turn before the departure is asked, the horse will push off the outside hind leg and depart on the outside lead. The rider must control the hindquarters through and after the turn, keeping them aligned under the horse's body, before the departure is asked. Rider timing matters significantly: asking for the departure before the horse has completed the full 180-degree arc and organized its body for the correct lead produces a rushed, unbalanced departure on whatever lead the horse's weight happens to be loaded on at that moment. Allowing the horse to complete the turn and arrive at a momentary balance point before the departure is cued gives it the physical opportunity to push off correctly. Hock or stifle soreness that makes pushing off the inside hind leg painful will also produce wrong-lead departures consistently and should be evaluated by a veterinarian when the problem persists despite correct rider preparation.