The Hottentot (1922)

A young man happens to have the same name as a famous steeplechase jockey, and when he finds out that people keep mistaking him for the jockey (although he's never been on a horse in his life and is actually terrified of them), he plays along with it, even going so far as to wear the same kind of racing togs that the real jockey wears. Eventually things get out of hand, and before he knows it he's forced to substitute in a race for the real jockey--and finds out that the horse he's supposed to ride is a ferocious beast called Hottentot.