The leg yield is a great exercise to work on suppleness and straightness of the horse. When first training a young or green horse, the leg simply means to go forward but as the horses’ training progresses and the aids become more sophisticated, the horse must also understand that the leg can mean to move sideways. Common mistakes in leg yield: 1. Horse speeds up onto a diagonal line and does not cross the hind legs or stay parallel to the rail. Correction: use the outside rein to stop the horse'