What is a Sportsbook?

A sportsbook is a gambling establishment where people can place wagers on a variety of sporting events. For many years, the only fully legal sportsbooks in the United States were located in Nevada, although they also operated in limited form in Delaware, Montana and Oregon before a 2018 Supreme Court decision led to their widespread expansion across the country. Many of these sites now offer an online presence that allows people to place bets from any computer or mobile device.

The most famous sportsbooks are located in Las Vegas, the betting capital of the world. When there are big sporting events, the sportsbooks can become crowded with people hoping to turn their sports knowledge into money.

To make a profit, the sportsbooks must be able to attract action on both sides of a game. They accomplish this by setting odds that will generate a return for them over the long term. The sportsbooks are free to set their lines and odds however they want, but most do so in a way that tries to avoid attracting too much action on one side or the other.

To do this, they use a metric known as closing line value. If a player’s wagers consistently provide better odds than they would have received betting the same sides before the game started, it is considered sharp action and they are quickly limited or banned by sportsbooks. To help protect themselves, sportsbooks keep a database of players and their betting habits that they use to determine how sharp they are.