Flyball races match two teams of four dogs each, racing side-by-side over a 51 foot long course. Each dog must run in relay fashion down the jumps, trigger a flyball box, releasing the ball, retrieve the ball, and return over the jumps. The next dog is released to run the course but can't cross the start/finish line until the previous dog has returned over all 4 jumps and reached the start/finish line. The first team to have all 4 dogs finish the course without error wins the heat. Jump height is determined by the smallest dog on the team – this dog, called the "height dog". NAFA is the North American Flyball Association http://www.flyball.org/index.html .