Answer:
to vault on a horse in mounted games or Prince Phillip cup games you have to get the horse/pony to trot alongside you when you are running at it's shoulder. then put your right hand on the pommel (the front of the saddle) and your left hand on the pony's mane. then face the front of the horse and jump along trying to swing your legs upover the saddle. keep praising the horse as you go along and talk to it. GOOD LUCK!!