Tracks employ a “linemaker” who sets the morning-line odds. But ultimately the bettors decide the odds based on who they put their money on.
The linemaker’s job is not to predict the outcome of a particular race, but to try to anticipate how the public will perceive the race. That’s an important distinction: The linemaker may know that a particular first-time starter has been working lights out but put that horse’s opening odds higher than a horse conditioned by a big-name trainer, figuring the public will gravitate toward that horse at the betting windows.
As betting begins, the odds begin to fluctuate based on the wagers that are being made. So if the word is out on that first-timer, for example, it may open up as the heavy favorite at odds of 3-5. But as post time draws closer, the public at large may begin to pour in money on that big-name trainer’s horse, dropping the odds on that horse and increasing them on the first-timer. By the time the gates open, the big trainer’s horse could be the 8-5 favorite, with the first-timer now an attractive bet at 5-2.
That’s why experienced horse players always pay attention to the Tote board during the half hour or so leading up to a race before deciding where to put their money.