Sports Betting

Sports betting is the placing of money on the outcome of a sporting event, or on something that happens during it, such as the first goal scorer or the number of points scored. Most bets are made with a bookmaker (a sportsbook) that sets odds and takes the other side of the wager; others are matched between bettors on a betting exchange. Sports betting takes place in shops, at venues and, increasingly, through websites and apps as part of online gambling (iGaming).

It is one of the oldest forms of gambling and one of the most widely legalised. Operators need a sports betting gambling licence in the markets they serve, and many countries license betting while restricting online casino games. Sports betting overlaps with financial speculation: odds behave like prices, betting exchanges resemble an order book, and prediction markets list contracts on sports outcomes, which has blurred the line between gambling law and derivatives regulation.

A sports bet is a small, one-off contract: "if this team wins, you pay me this much; if it does not, I keep my stake." The odds are the price of that contract. Short odds mean the bookmaker thinks the outcome is likely, so the payout is small; long odds mean the reverse.

A bookmaker is like a shop that buys and sells umbrellas on both sunny and rainy days. It does not need to know the weather; it sets its prices so that, whatever happens, the money from one group of customers covers the payouts to the other, with a little left over. That leftover is how the bookmaker earns a living.

Odds can be quoted as decimals (2.50), fractions (6/4) or American "moneyline" numbers (+150). Decimal odds include the stake: a 10-unit bet at 2.50 returns 25. Each decimal price implies a probability:

Here $p$ is the implied probability and $d$ is the decimal odds. Across all outcomes of an event, the implied probabilities add up to more than 1; the excess is the bookmaker's margin, called the overround or vig:

Here $d_i$ is the decimal price of each possible outcome $i$. Worked example: a tennis match priced at 1.91 for each player. Each implied probability is $\frac{1}{1.91} \approx 0.5236$, the sum is about 1.0471, so the overround is about 4.7%. If the bookmaker takes equal money on both players, it pays out 1.91 per unit staked on the winner while collecting 2 units in total, a gross margin of about 4.5% of turnover.

• Fixed-odds bets. The price is fixed when the bet is placed, the standard bookmaker model.
• In-play bets. Wagers placed while the event is under way, with prices updated continuously from data feeds.
• Accumulators and parlays. Several selections combined into one bet, which multiplies both the odds and the bookmaker's margin.
• Pool (pari-mutuel) betting. Stakes go into a pool shared among winners after a deduction, common in horse racing.
• Exchange betting. Bettors back and lay outcomes against each other, and the exchange charges commission on net winnings rather than taking a position.

Sports spread betting, where the payout depends on how far a result differs from a forecast, can multiply losses in the way that leverage does in trading.

National approaches vary widely. Great Britain licenses betting through the UK Gambling Commission (UKGC); Malta's operators are licensed by the Malta Gaming Authority (MGA). In the United States, a 2018 Supreme Court decision (Murphy v. NCAA) struck down the federal law that had confined sports betting mostly to Nevada, and most states have since legalised it in some form. In 2025 some prediction markets regulated by the Commodity Futures Trading Commission began listing sports event contracts, prompting disputes with state gambling regulators. Brazil licensed fixed-odds betting from January 2025, then prohibited it by presidential provisional measure in September 2026, pending congressional review. Sites holding only an offshore gaming license face geo-blocking orders and payment blocks in licensed markets.

Integrity is a specific concern. Match-fixing and spot-fixing use betting markets to profit from manipulated events, a form of market manipulation. Operators and sports bodies share data on suspicious betting patterns, and the Council of Europe's 2014 Macolin Convention addresses the manipulation of sports competitions.

Betting accounts are funded by cards, e-wallets, bank transfers and instant payment schemes, and withdrawals return winnings to the player. Payment providers treat betting as a high-risk merchant category with its own merchant category code (MCC) and specific rules covered under gaming payments. Money launderers may bet on all outcomes of an event to lose only the margin while turning cash into apparently legitimate winnings, so operators apply know your customer (KYC) checks, source of funds reviews for high stakes and transaction monitoring under anti-money laundering (AML) law. Public health concerns centre on in-play betting, heavy advertising and sponsorship, and losses among young men. Where licensed betting is banned, demand tends to shift to unlicensed sites and the grey economy.

• Gambling Commission (Great Britain)
• Secretaria de Prêmios e Apostas (Brazil, Ministry of Finance)