139. Sports betting

Sports betting is the general activity of predicting results by making a wager on the outcome of a sporting event. Perhaps more so than other forms of , the legality and general acceptance of sports betting varies from nation to nation. In the United States, the Professional and Amateur Sports Protection Act of 1994 makes it illegal to operate a "betting, gambling or wagering scheme", except for in the states of , , and . Nevada, however, is the only state currently allowing sports gambling, while in many European nations (the profession of accepting sports wagers) is highly regulated but not criminalized.

Proponents of legalized sports betting generally regard it as a hobby for sports fans that increases their interest in particular sporting events, thus benefiting the leagues, teams and players they bet on through higher attendances and television audiences. Opponents fear that, over and above the general ramifications of , it threatens the integrity of amateur and professional , the history of which includes numerous attempts by sports gamblers to , although proponents counter that legitimate bookmakers will invariably fight corruption just as fiercely as governing bodies and law enforcement do. Most sports bettors are overall losers as the bookmakers odds are fairly efficient. However, there are professional sports bettors that make a good income betting sports.

Aside from simple wagers--betting a friend that one's favorite team will win its division, for instance, or buying a football "square" for the --sports betting is commonly done through a . Legal sports bookmakers exist throughout the world (perhaps most notably in ). In areas where sports betting is illegal, bettors usually make their sports wagers with illicit bookmakers (known colloquially as "bookies") and on the , where thousands of online bookmakers accept wagers on sporting events around the world. (In the United States, the legality of wagering is ambiguous, due to the fact that online bookmakers generally operate outside of the U.S. Some online bookmakers do not accept wagers from the U.S. due to these unresolved legal questions.)

The bookmaker earns a commission or by regarding the money at risk as less than the size of the bet placed. A common line is a $110 bet on a fair coin which pays $210 to win and $0 to lose. On this line, it costs $220 to bet both sides of the same coin simultaneously, but the combined bet always pays $210. The $10 loss constitutes the vig. There are opposing positions on whether the winner or loser can be construed as paying the vig, but this debate is not especially meaningful. If you view $110 to win $210 on a fair coin as $100 at risk, then it will appear as if the loser pays the vig; if you view the same line as $110 at risk, then it will appear as if the winner pays the vig. It happens that standard practice among bookies is to adjust odds so the amount at risk remains constant from the winning side of the proposition, hence the common perception that the loser pays the vig. Vigs expressed as percentages suffer from the same perceptual bias. On the line as given in this example, for a fair coin, the bookie has an expectation of making $5 for each $110 bet placed, which is often divided out and expressed as 4.5% Odds on teams or adversaries are quoted in terms of the favorite (the team that is expected to win, thus requiring a riskier wager) and the underdog.