Flyball is run in teams of four dogs, as a relay. The course consists of four hurdles placed 10 feet (3 m) apart from each other, with the starting line six feet (1.8 m) from the first hurdle, and the flyball box 15 feet (4.5 m) after the last one, making for a 51-foot (15.5 m) length. The hurdle height is determined by the height of the smallest dog in the team. Under current North American Flyball Association (NAFA) rules this should be 5 inches below the withers height of the smallest dog, to a height of no less than 7 inches (20.3 cm) and no greater than 14 inches. Under current United Flyball League International (U-FLI) All eligible dogs shall have a recorded jump height of 12". Dogs will be measured from the point of the elbow to the Accessory Carpal Bone (Pisiform), the bony protrusion just above the stop or carpal pad. The smallest dog, to a height of no less than 6 inches and no greater than 12 inches. Each dog must return its ball all the way across the start line before the next dog crosses. Ideal running is nose-to-nose at the start line. The first team to have all four dogs cross the finish line error free wins the heat. Penalties are applied to teams if the ball is dropped or if the next relay dog is released early.