As it has happened so often, a horse wins the first two legs of the Triple Crown, and comes into the Belmont with a huge amount of attention, a target on its back, and historic levels of fame if it can pull off the final victory.
With all that attention comes a lot of extra money being bet on the races. The amount of money bet on Saturday's Belmont Stakes might be around $200 million—multiple times higher than what the entire nation's worth of horse races get bet on a normal Saturday.
This huge spike is basically the "dumb money"—people who make a wager on a Triple Crown race who otherwise don't know what they are doing.