Deliberate mistake: In the final race of the film, Seabiscuit performs a flying lead change at the gallop while crossing the finish line, in the famous shot taken underneath his neck. Horses normally only switch their leads around turns while racing; it's something done to relieve pressure on the leading foot. From taking the shot over and over again, the horse playing Seabiscuit was probably tired out and a little tender and began to perform lead changes in other places in an attempt to be more comfortable.