I would assume any sport can add too, just not take away. For instance Endurance racing, a race may have multiple sanctioning bodies. Take a recent ride for instance, sanctioned by FEI,,, AERC and SERA, and run by a ride manager, FEI says helmet not required, AERC (American national body) says, Jrs required, SERA, (regional) says everybody wears one (example not sure if it does or not) See it isnt violating FEI rules for a lower level organization to require one. The lower orgs have "Added to". So even though FEI can say not required an organizer can still require it. I would guess sooner or later they are going to be required to get any kind of liability protection.