In a leg yield, the horse moves away from the bend and steps its hind leg under its belly and toward the opposite front leg. It is important to keep the horse fairly straight from ears to tail. Introducing the leg yield along a fence line or arena wall is helpful for the horse to learn the exercise. Once the horse understands leg yield at a walk along side the wall or fence line at a walk, it can be introduced from the quarter line to the wall or fence line.
After the horse understands leg yield with rhythm, balance and relaxation, you may introduce leg yield in flat walk. Begin with a couple steps of leg yield at a flat walk and then proceed in a straight line. Increase the number of leg yield steps until the horse is able to travel gradually from the quarter line to the fence (or arena wall).
Horses tend to over bend the neck or lead with their shoulders as they learn the leg yield. Keep the horse straight by using the inside leg at the girth and maintain contact with the outside rein to keep the outside shoulder straight. If the horse gets stiff in the jaw, use your inside fingers and massage the rein and release to encourage a soft contact.
Video: Leg yield at a Flat Walk