What is a Sportsbook?

A sportsbook is a gambling establishment that accepts bets on various sporting events. They make money by charging a commission or “vig” on each bet placed. This ensures they will earn a profit over the long term. Sportsbooks can also be found online and are quickly becoming more popular with the legalization of sports betting in many states following a Supreme Court decision in 2018.

To place a bet at a sportsbook, you must present cash or a credit card to the cashier. They will then print out a ticket that shows you have a wager on that game. Keep this ticket because it will be required to cash out your winnings at the end of the day. It is also useful for keeping track of your units (the amount of money a bettor places on one game) throughout the day.

Betting lines move a lot, especially when bettors are aggressive or known to win. For example, if a team’s starting quarterback gets hurt in practice four days before a game, the sportsbook will take that game off the board until they have more information. The line will then reappear later that afternoon, often with sharper limits to accommodate the action from bettors they know are winners.

Professional bettors prize a metric called closing line value, which is the final odds posted before the game starts. It is a strong indicator of how sharp a bettor is because the higher the closing line value, the more likely it is that the bettor will show a long-term profit.