I know a bit about cowboying, a bit about FFA:
Folks slide on over on the web to why bulls and horses buck at rodeos
Critters are born with the instinct to flee from danger; that's about the only defensive behavior horses have, it's in their genes.
If a cougar jumps on a horse's back, the only defensive behavior he has is to run and buck. (that is rare today, only because most of the cougars have been killed.).
No critter likes to be confined.
When you put a flank strap on him, then a cowboy crawls onto his back, he will buck, buck, buck... (A flank strap has nothing to do with *******s, no way)
Horses, bulls are not harmed, or mistreated, they are made very uncomfortable for
9 seconds-that's about it.
Bulls require a different post, as does Future Farmers of America