County Fair (1950)

"Ma" Ryan, who runs a burger stand at the county fair, asks daughter Loretta to put a bet on a horse that Loretta's boyfriend Tommy is riding. Unfortunately, Loretta mistakenly places the bet on the wrong horse. When she discovers her error she tries to get the cashier to exchange the ticket for the horse she wanted, but the cashier refuses. Peter Brennan, standing in back of her in line, buys the ticket for the horse Loretta wants and then exchanges it with her. It turns out that Peter is from a wealthy family that owns racehorses, and Peter is a horse trainer himself. He soon begins to fall for Loretta, and Tommy doesn't like it one bit. Complications ensue.

Unfortunately the movie County Fair is not yet available on HBO Max.