“They know how important betting is to their sport, and more importantly, the betting industry knows how important football is to it,” said Borod, who has worked in the sports betting field for nearly a decade. “In the early days, there was a view that maybe you shouldn’t be able to bet at a sports book inside the stadium. But I think as sports betting has matured, and you realize, well, people are doing it on their phones anyway.”

The sports book, which is open only to ticket-holders during Commanders games, does not have a view of the field, so by kickoff of Sunday’s game with the Arizona Cardinals, only five people lingered inside on the leather couches and at the bar. At halftime, there was a steady trickle of fans, some returning to place bets based on what they had seen in the first half. Others sought a cool, dry place to order food and drinks.

“Doubling down on Washington, huh?” a fan wearing the jersey of Kamren Curl, the Commanders safety, called out to another bettor at the next kiosk over. Washington trailed the Cardinals by 3 points at halftime, but he reasoned that the home team wasn’t likely to give away the ball three more times. Another Commanders fan, standing under a television screen that displayed live odds for all of the early afternoon N.F.L. games, begrudgingly put money on the Cardinals.

Joe D. and Jason B., two childhood friends attending the game to celebrate their birthdays, had already placed bets on a mobile app leading up to Sunday’s game. But when they saw the sign outside the sports book offering a free hat, they decided to venture inside where each put down $20 more, less than the cost of any hat at the Fanatics apparel store next door.

“We never put in money we don’t have,” said Jason B., who along with his friend declined to give his last name, citing a societal stigma around gambling. “But not everyone has the ability to control themselves.”