In the coming days, the country’s best men’s and women’s college basketball teams will clash in the N.C.A.A. tournament finals. For fans, these are some of the biggest events of the year — a chance to see the best young athletes in the highest-stakes games. They are also some of the most lucrative events for sports betting apps. Americans will legally wager nearly $3 billion this year during March Madness, the American Gaming Association estimates.

Six years ago, sports betting was illegal under federal law. Today, it is everywhere. N.B.A. and N.H.L. viewers are exposed to three gambling ads a minute, a recent study found. Commercial sports betting revenue has increased 12-fold since 2019, as this chart by my colleague Ashley Wu shows:

What happened? In 2018, the Supreme Court struck down a federal ban, concluding that it violated states’ rights. Thirty-eight states and the District of Columbia now allow gambling on games.

The old laws were strange in many ways. Other countries had allowed betting. The U.S. allowed it for some competitions, like horse racing. And millions of Americans were already betting on sports, regardless of its legality.

But the Supreme Court did not just let Americans place legal wagers. It also empowered a big industry to market sports betting apps and convince more people to gamble, through another set of rulings.

Enabling big business

Americans typically learn about free speech in the context of social and political issues. But starting in the 1970s, the Supreme Court has interpreted the First Amendment to protect advertisements. Now, if something is legal, it can be advertised, and governments can’t stop companies from marketing it. (There are some limits: Ads can’t be deceptive or misleading, for instance.)

Supporters of this legal paradigm say that advertising lets consumers make informed decisions. “The court has taken the view that the freedom of speech, generally speaking, should let individuals decide for themselves what to believe without the government trying to say that these are bad messages,” Eugene Volokh, a legal scholar at U.C.L.A., told me. In other words: If people want to spend their savings on legal sports wagers, they should be able to find out how to do so.

What about tobacco? It’s true that cigarette companies are not allowed to advertise, even though their products are legal. But this is a special situation. Executives agreed not to market cigarettes as part of an unusual legal settlement with states in 1998. Otherwise, the Supreme Court has upheld tobacco companies’ right to advertise on First Amendment grounds.

The rulings mean that the only reliable way to prevent the mass marketing of a product is to ban it. For lawmakers, “there is this strange incentive to try to get around the First Amendment by not legalizing things or by banning products,” Jennifer Pomeranz, a public health lawyer at New York University, said. She pointed to the federal government’s prohibition of marijuana, even as many states have legalized the drug.

The consequences

The American Gaming Association says that sports betting ads guide people from illegal to legal markets, which raises tax revenue for governments and helps consumers avoid fraud.

But advertising also convinces more people to gamble. Recovering addicts complain that the deluge of ads presents a constant temptation when all they want to do is watch a game. Calls to gambling helplines have increased in states that legalized sports betting.

Legal gambling has also affected the sports themselves. Consider prop betting, in which people try to predict how an athlete will perform in a given game. Fans have threatened players who don’t meet their predictions. And athletes can bet on themselves, then adjust their play in an effort to cash out, as N.B.A. player Jontay Porter has been accused of doing. Such self-dealing could damage the integrity of a competition. For these reasons, Louisiana this week passed a ban on prop betting for college athletes.

Gambling can also bring other kinds of headaches for athletes. Baseball superstar Shohei Ohtani is currently mired in a scandal after his former interpreter allegedly stole millions to pay for bets. (That misconduct involves illegal betting markets. The Athletic explained how they work.)

These issues will become more common as sports betting grows. But the gambling industry has a vested interest in getting as many people to participate as possible, regardless of the consequences. And as a result of Supreme Court rulings, lawmakers are limited in what they can do.

For more: Ohtani is performing, despite the gambling scandal. He hit his first home run as a Dodger with a 430-foot shot. See fun images of his fans.

THE LATEST NEWS

Israel-Hamas War

• Israel agreed to open a crossing to increase humanitarian aid to northern Gaza after President Biden called Benjamin Netanyahu and threatened to make U.S. support conditional on civilian protections.

• Donald Trump again urged Israel to quickly end the war, saying, “I’m not sure that I’m loving the way that they’re doing it.”

• Benny Gantz, a political rival to Netanyahu, called for early elections in September. It’s a sign that the war is straining Israel’s unity government.

More International News

Scotland: A Willy Wonka event ended in disaster. From its ashes rose a budding star.

36 Hours: Fly kites on the lawn of a fortress and explore mural-lined streets in San Juan, P.R.

Celestial event: Animals could act strangely during the solar eclipse.

Lives Lived: Gaetano Pesce hated right angles. A rebel designer of furniture and art objects, his most celebrated work was an armchair shaped like a fertility goddess that represented the subjugation of women. Pesce died at 84.

SPORTS

College basketball: The most anticipated women’s Final Four in history begins tonight, with Iowa and Caitlin Clark serving as headliners alongside undefeated South Carolina.

North Carolina: The N.C. State women’s and men’s basketball teams are both in the Final Four. That’s a boon for Raleigh.

Title game: Want to go to the women’s NCAA championship? It’ll cost you close to $1,000 — a bit more than the men’s.

M.L.B.: The Oakland Athletics reached a deal to play in Sacramento for the next three seasons before the team’s planned move to Las Vegas in 2028.

N.B.A.: Knicks forward Julius Randle will miss the rest of the season with a shoulder injury.

ARTS AND IDEAS

Fashion and sports: Days after L.S.U. lost to Iowa in the Elite Eight, the team’s star forward Angel Reese was still making headlines — this time in Vogue.

She used the magazine to announce she would enter the W.N.B.A. draft and posed for a shoot with clothes from Valentino, Diesel, Wales Bonner and Christian Louboutin — the latest expression of a growing overlap between fashion and sports. The Paris Olympics this summer will be the ultimate mixing of these industries, Vanessa Friedman writes.