but these things DO matter cocker_luva, if they dog is to small it cant safley jump the hights requred in flyball, structer also matters, if say they have bad shoulders, or some other problem of the sort they can hurt themselves, body type matters because agility and flyball require a lot of jumping, a bulky dog will have more problems then a thin narrow dog, because the bulky dog has a lot more pressure placed on there shoulders when they jump. I longer muzzle is better because they need to be able to breath very well, that much running and jumping is exuasting, and the dog needs to be able to keep good air flow. these things are not for the purpose of the dog being the best or anything, its all for the safty of the dog, preformance bred dogs have there structurs evaluted several times through puppy hood to make sure that the sports wont cause then problems or injury.