For a century following the Black Sox scandal of 1919, when Major League Baseball players conspired with gamblers to lose a championship series, American sports leagues opposed betting as a threat to their integrity. In 2012 Bud Selig, then MLB's commissioner, said that gambling was "the deadliest of all things that can happen…It creates doubt and destroys your sport."
In 2018 the Supreme Court ruled that a federal prohibition against sports betting was unconstitutional. Since then 39 states have legalised the activity; on December 1st 2025 Missouri became the latest to do so. Industry supporters argue that prohibition did not prevent earlier wrongdoing and that legal sportsbooks, by monitoring for suspicious wagers, can aid enforcement. On the other hand, mass-market gambling increases the number of potential conspirators and eliminates the stigma about players consorting with punters.
The effects of legalisation have been especially intense on college campuses. A survey conducted in 2023 by the NCAA found that 60% of college students have gambled on sport, with the share even higher among those living on campus. The NCAA survey also found that 16% of 18-to-22-year-olds engage in problematic sports gambling. A poll by Siena University in January 2025 found that a quarter of men who have gambled on sports say a friend or family member has expressed concern about their betting, and 28% of 18-to-34-year-old men who use sports-betting apps said they had had trouble meeting a financial obligation because of a lost bet. Timothy Fong, a professor of psychiatry at the University of California, Los Angeles, says every one of his recent clients has been an 18-to-24-year-old man seeking help for a sports-betting or cryptocurrency addiction.
"Player props"—bets on an individual player's statistical performance—have surged in popularity. They are uniquely appealing to match-fixers, since they require only a single player's participation and can usually be manipulated without affecting a game's outcome. Their growth has led to verbal abuse and occasional threats aimed at players, including college athletes as young as 18, from bettors with a financial stake in those athletes' numbers.
"Same-game parlays" (SGPs) let users combine multiple bets into a single high-risk, high-reward wager, increasing the potential profits for those with inside information. Only big companies can afford to offer enormous payouts on SGPs. Sportsbooks are loth to scrap props entirely because SGPs, typically laden with props, are their most profitable product.
Charlie Baker, president of the National Collegiate Athletic Association, has long called for a ban on props in college sports. Adam Silver, the NBA's commissioner, has advocated eliminating them for bottom-tier NBA players. Limiting props to prominent professional players—who draw the most interest from recreational bettors and stand the most to lose from being caught—might be a sensible compromise.
In 2007 Tim Donaghy, an NBA referee, admitted to betting on games where he had officiated. In 2024 Jontay Porter, an NBA player, was arraigned for a scheme in which he repaid gambling debts by leaving a game early so that "under" bets on his statistics would win. In October 2025 prosecutors indicted Terry Rozier, a mid-tier NBA player, and Chauncey Billups, a Hall of Fame member and coach of the Portland Trail Blazers. Mr Rozier was accused of telling a friend he would remove himself from a game shortly after it began; the friend allegedly sold this information to gamblers. Mr Billups was charged with playing in a rigged poker game run by the Mafia and, in a separate allegation, informing gamblers that he planned not to play his team's stars in an upcoming game.
Betting firms deploy complex "player profiling" to identify and restrict winning bettors ("sharps"). A good profiling strategy can boost a firm's margins by 10-20%. Britain's Gambling Commission found in 2025 that 4.3% of active accounts have reduced stake factors; in Massachusetts only 0.64% are limited.
Profiling begins before a bet is placed: computer vs phone, debit card vs e-wallet deposit, gender (women are flagged as suspicious, since many sharps use women as proxies). The key metric is "closing-line value" -- whether the odds at which a bettor wagers consistently beat the closing price. If a player is ahead of the market over his first ten wagers, he is highly likely to beat the book long-term. Sportsbooks monitor "risk scores" every six to eight hours.
Sharps evade restrictions through "beards" or "mules" (proxy bettors), "priming" (intentionally making large losing bets to raise an account's limits), and "whale-flipping" (hiding shrewd bets in a big loser's account). Billy Walters, perhaps the most successful American sports bettor of modern times, wrote that golfer Phil Mickelson routinely placed wagers for him at vastly higher limits.
Every Australian state has set minimum amounts punters must be allowed to win on horse and greyhound races, usually A$2,000. In Spain, thousands of bettors have won lawsuits requiring operators to reset their stake factors. Britain's Gambling Commission noted in July 2025: "Being a successful bettor is not a protected characteristic in discrimination law."
By the end of 2026, 40 states will have legalised sports betting and 11 will allow "i-gaming" (online slots and table games). Some 17% of Americans bet on a sporting event in 2025, more than double the share two years earlier, according to polls by Ipsos. Half of American men under 50 have an online sports-betting account. Most of the online market has been seized by two digital upstarts, DraftKings and FanDuel, though Las Vegas bookmakers such as MGM and Caesar's Palace have set up their own betting apps, using loyalty points redeemable in their casinos to draw online customers into their physical resorts.
The NBA's structure exacerbates vulnerabilities. Title contenders generally rest players to keep them healthy for the playoffs, while teams that miss the playoffs are actually rewarded for losing, because those with the worst records have the best odds of winning the draft lottery. Many teams routinely rest their best players during the final months of the regular season, making betting markets revolve around inside information on stars' availability.
Before borrowing money from a friend, decide which you need more.