The National Football League (NFL) kicked off its 100th season on Thursday night with a game between one of the league's longest rivals, The Green Bay Packers and The Chicago Bears. On Sunday, the rest of the Week 1 games were played between the other 30 league teams. As legal sports betting grows across many US states, this new multibillion dollar activity has the potential to change the landscape of American football consumption like never before.

Sports betting in the US had been illegal since the 1992 Professional and Amateur Sports Protection Act (PASPA). But last May the Supreme Court took up a case brought by National Collegiate Athletic Association and the four major professional sports leagues challenging a New Jersey law that legalized sports betting. The leagues argued that the state law violated PASPA, but the Supreme Court disagreed and ruled 6 to 3 in favor of New Jersey. The Court cited the 10th Amendment and anti-commandeering doctrine, which means Congress cannot directly order states to take actions. Thus, legal sports betting became an option in all 50 states, depending on state law and the legislature's desires.

Along with a recovery in ratings last year and an average 15.8 million viewers per game, the centennial NFL season could shape up to be the league's most lucrative.

Before the ruling, US bettors needed to either travel to Las Vegas or use offshore online betting services like Bovada that only accept cryptocurrency. Now sports betting is legal in 13 states. Of course, people can still play fantasy football in states where sports betting remains illegal.

The American Gaming Association estimates that 7 million Americans will legally bet on NFL games at in casinos, while thousands more will join online betting pools and friendly wagers this season. For casual and serious bettors, the IRS requires that winnings over $5,000 and 300 times the original bet be withheld by the casino at a 24% rate. Bettors can also write off gambling losses up to their amount of winnings in the tax year if they itemize deductions, and professional gamblers can deduct travel expenses as losses. Casinos will send out a W-2G tax form if a bettor wins at least $600. The IRS treats any income from gambling as taxable income.

The effect of legal sports betting on the NFL is unclear at the moment because television contracts with Fox (FOXA  ), CBS (CBS  ), NBC, and ESPN prohibit announcers and pundits from discussing gambling. In addition, the TV networks are ensuring viewers do not get overwhelmed with commercials related to sports betting by monitoring and capping ad loads. The NFL's official position is that the sports gambling landscape is young and it does not want to irritate consumers who dislike betting. Still, last month the league expanded its partnership with Sportsradar, a sports data firm, and Dallas Cowboys owner Jerry Jones said legal sports betting will boost the value of NFL TV rights by 50%. Even if he is wrong, the NFL rakes in $5 billion annually from its TV deals, so before the deals expire in 2022, the US expansion of legal sports betting could make the league much more valuable.

The author does not hold any positions in any of the securities above.