Sportsbook

A sportsbook is a business, or the product it runs, that accepts and settles bets on the outcomes of sporting events.

Definition

A sportsbook sets odds (prices) on events across sports such as football, tennis, and horse racing, takes stakes from customers, and settles winning and losing bets once results are confirmed. Its built-in margin — called the overround or vig — is baked into those odds so the implied probabilities of all outcomes sum to more than 100%, giving the operator a theoretical edge over the long run rather than on any single event. The term describes both the licensed company (the bookmaker) and the betting product itself, whether delivered in a retail shop, online, or via a mobile app. A sportsbook may compile and manage its own prices or rely on third-party trading, odds, and data providers.

Worked example

Take a two-way market with each side priced at 1.90 (decimal). Each price implies a probability of 1/1.90 ≈ 52.6%, so the two sum to about 105.3% — that ~5.3% excess is the overround. A £10 winning bet at 1.90 returns £19 (£9 profit), while a £10 losing bet returns nothing. If the book is balanced — say £100 staked on each side, £200 in total — the operator pays the winners £190 and keeps £10, a 5% hold that does not depend on which side wins.

Why it matters

The sportsbook is the core product of the sports-betting vertical, so understanding it underpins everything from odds compilation and risk management to responsible-gambling controls and licensing. For operators, sustainable revenue comes from accurate pricing and margin management across many events, not from any single result. For learners, seeing how the overround works clarifies why betting is structured as paid entertainment with a built-in house edge — not a source of income.

Related

Note: Stable definition. Terminology varies by region: "sportsbook" is standard in the US, while "bookmaker" or "bookie" dominate in the UK and Ireland. Licensing requirements, permitted markets, in-play rules, and margin/tax treatment vary by jurisdiction and operator.