What is Book (Sportsbook)?

A sportsbook, often called simply 'the book', is a company — online or physical — that accepts wagers on sporting events, sets the odds, manages its risk through line movement and profits from the vig (the margin baked into its prices). Major online sportsbooks include Bet365, DraftKings, FanDuel and William Hill. The operator that sets the lines is also referred to as 'the book', and when a bettor 'beats the book' they win more than expected over a long run of wagers. A sportsbook's core job is balancing its book: it wants roughly equal money on both sides of a market so that the losers pay the winners and the operator keeps the margin regardless of the result. It moves lines to attract action to the under-backed side. Worked example: a sportsbook opens a match at 1.91 on each team, which corresponds to implied probabilities of about 52.4% each — a total of 104.8%, the extra 4.8% being the vig. If heavy money lands on the favourite, the book shortens that price to, say, 1.80 and lengthens the other side to 2.02, nudging bettors toward the neglected team to rebalance its liability. The common misconception is that a sportsbook is betting against you and 'needs you to lose'. In its ideal scenario it is indifferent to the outcome and simply collects the margin on balanced volume. Bettors who consistently beat the closing line are the ones the book genuinely fears, and such accounts are often limited. Compare with bookmaker, vig and the closing line.