Teams of horses and riders in matching costumes move around a ring, performing steps and motions perfectly choreographed to music that they have practiced for months, even years. Some riders even dare to perform gymnastics on top of the moving horse during their routines in the Dancing Horse Challenge, the star event of the 10th annual Ride for Life scheduled for this weekend at the Prince George’s Equestrian Center in Upper Marlboro. “The horses actually dance,” event publicist Caryn Sagal said. “It’s a really unique event.”