Chalk in thoroughbred horse racing refers to the betting favorite in a race, particularly when that horse is a heavy or strong favorite. A “chalk player” is a gambler who consistently wagers on favorites rather than longshots. While betting the chalk offers a higher probability of winning, it also means lower payouts due to the short odds.
The term originated directly from horse racing in the early days when odds were displayed on chalkboards rather than digital screens. Since favorites attracted more betting action, their odds had to be updated more frequently as money poured in. Bookmakers constantly erased and rewrote the favorite’s odds with chalk, which resulted in the favorite’s section of the board becoming covered in chalk dust.