horseplayer 
noun North American
A person who regularly bets on horse races.Continuing to show a preference for out-of-state racing, Maryland horseplayers continued the trend of abandoning the local product in favor of simulcast wagering....
- Paul Makin, the managing partner of the syndicate that owns Starcraft, made his fortune as a professional horseplayer on races in Hong Kong and Japan.
- If a horse works fast in the morning, he will usually take action on the tote board in the afternoon from the average horseplayer, who has little else to go on.