Flyball is a relay race with 4 dogs racing, 2 "spare" dogs and their handlers on each team.
The course consists of a starting line, 4 jumps ( hurdles ) spaced 10 feet apart and a box. The first hurdle is 6 feet from the start line and the box is 15 feet from the last hurdle for a 51 foot overall length.
The dogs run down the lane, jumping over the hurdles and step on a spring loaded box that shoots out a tennis ball. The dog catches the tennis ball and then runs back over the hurdles. When the dog crosses the starting line the next dog goes. The first team to have all 4 dogs run without errors wins the heat.
The height of the hurdles is dependent on the height of the shortest dog running in the heat.