Why is it whenever we watch horse racing, whether thoroughbreds or harness racing or even car racing, why is it that all racing goes counterclockwise?
It all goes back to England.
According to Tom Gilcoyne at the National Museum of Racing and Hall of Fame in Saratoga, N.Y., horse racing in this country during colonial times was run clockwise, or "right-handed" (all right-hand turns). But during the American revolution, that English custom was deliberately replaced by left-handed track races like the ones we see in America today.
In England 30–40% of races are now run the same way ours are. In central Europe, however, most are run right-handed.
Incidentally, Man o' War's victory at the 1920 Belmont Stakes was run right-handed. The Belmont was run that way from its first season at Belmont Park in 1905 until 1921.
—The Fact Monster