TJ is right. Polynesian, the 1947 American champion sprinter, suffered an attack of azoturia, or "tying up" as a 2-year-old. While he recovered from his illness, he developed a phobia about moving, apparently fearing that it would cause him pain. A hornet attack in his paddock started him running again. He was never enthusiastic about training, to the point that he ran most of his races when no more than half-fit, but his raw talent was right up there with the best.
I'm Avalyn Hunter, an author, pedigree researcher and longtime racing fan with a particular interest in Thoroughbred mares and their contributions to the history of the breed.