As recently as three years ago, sports betting was considered taboo. Now, 45% of American adults live in a state where it's legal.

The state of play: 25 states and Washington, D.C., have legalized sports betting, and 21 of those markets (plus D.C.) are live and operational.

Why it matters: March Madness is the biggest sports betting event of the year in the U.S., beating out the Super Bowl due to the sheer volume of games.

• The sports betting industry took a huge hit when last spring's NCAA Tournament was canceled along with most other sports.
• But it has rebounded in a major way, with legal betting revenue reaching $1.5 billion in 2020 and projected to hit $3.1 billion in 2021.
• 100 million Americans can now legally bet in their home state, a 74 million jump from the 2019 tournament.

Less brackets, more bets: Filling out a bracket is an annual tradition that will never go away. But the rise of legal sports betting could steal some of the attention away from office pools.

• 36.7 million Americans will fill out a bracket this year, down 8% from 2019, according to a new American Gaming Association study.
• 30.6 million Americans plan to place more traditional bets this year, a 72% increase from 2019.

The backdrop: Given the stigma that was long attached to sports betting, the speed at which it has been normalized and gone mainstream is astounding. A brief history of sports betting in this country...

• 1931: Nevada opens the nation's first casinos in an attempt to avoid bankruptcy. "Any state could have done it," UNLV professor Anthony Cabot told NYT. "But no others did."
• 1949: Sports betting becomes explicitly legal in Nevada.
• 1978: Casinos open in Atlantic City, New Jersey.
• 1988: Congress passes the Indian Gaming Regulatory Act, permitting casinos on land owned by Native American tribes.
• 1992: Congress passes the Professional and Amateur Sports Protection Act (PASPA), which bans sports betting nationwide beyond a few exceptions like bike racing in New Mexico and bookmaking in Nevada.
• 2018: In May, the Supreme Court strikes down PASPA, determining it to be unconstitutional.