"The 2021 NCAA Tournament will be the most widely bet-on sporting event in U.S. history," said Eric Ramsey, analyst for PlayUSA.com. "The popularity of the NCAA Tournament combined with such a high number of games typically makes March Madness the largest sports betting holiday each year in terms of handle, and there is no reason to suspect that won't be the case this year. But the number of legal sports betting markets has more than tripled since 2019 and we are still in the midst of a pandemic that could slow retail sportsbooks. Those reasons alone make this year difficult to predict."

The last time the NCAA Tournament was played in 2019, bettors in seven states could place a wager legally. Those seven states, which includes today's three largest markets, New Jersey, Nevada, and Pennsylvania, as well as Delaware, Mississippi, Rhode Island, and West Virginia, managed to generate an estimated $440 million in bets, or about 40% of the nation's overall handle in March, according to PlayUSA.

Now with 20 states and Washington D.C. offering some form of legal sports betting, the U.S. landscape has shifted dramatically.

Today, an adult population of about 86 million can now bet legally in their home states. In 2019, about 26 million adults enjoyed access to legal sportsbooks in their home states.

"The Super Bowl draws the most bets for a single game, but March Madness and its 60+ games should more than double what the Super Bowl draws," said Dustin Gouker, lead analyst for PlayUSA.com. "But the dramatic expansion of legal markets, as well as the exponential growth within each market, means more people will have an opportunity to bet on the NCAA Tournament than ever before. And that will produce an eye-popping handle number that could reach $1.5 billion."

2021 also brings multiple factors that will be unique to this year's tournament. For one, pandemic-related restrictions are still in place in many legal jurisdictions, and some bettors may still be hesitant to go indoors. That gives New Jersey, which generates more online wagering than any other state, an advantage. PlayUSA projects the Garden State will lead the U.S. with $300 million in NCAA Tournament betting.

In addition, for the first time in history every game of the NCAA Tournament will be played in a legal sports jurisdiction. With so many games being played locally, Indiana has the potential to far outperform what would normally be expected of the nation's fifth-largest U.S. sports betting market.

"With so many variables at play, this will be a fascinating NCAA Tournament to watch," Ramsey said. "We know that the tournament will draw heavy action. But it won't look like any NCAA Tournament that we have ever seen."