Sports betting is the activity of predicting sports results and placing a wager on the outcome. The frequency of sports bet upon varies by culture, with the vast majority of bets being placed on association football, American football, basketball, baseball, hockey, track cycling, auto racing, mixed martial arts, and boxing at both the amateur and professional levels. Sports betting can also extend to non-athletic events, such as reality show contests and political elections, and non-human contests such as horse racing, greyhound racing, and illegal, underground cockfighting. It is not uncommon for sports betting websites to offer wagers for entertainment events such as the Grammy Awards, the Oscars, and the Emmy Awards.
Sports bettors place their wagers either legally, through a bookmaker/sportsbook, or illegally through privately run enterprises. The term “book” is a reference to the books used by wagebrokers to track wagers, payouts, and debts. Many legal sportsbooks are found online, operated over the Internet from jurisdictions separate from the clients they serve, usually to get around various gambling laws (such as the Unlawful Internet Gambling Enforcement Act of 2006 in the United States) in select markets, such as Las Vegas, Nevada, or on gambling cruises through self-serve kiosks. They take bets “up-front”, meaning the bettor must pay the sportsbook before placing the bet. Illegal bookies, due to the nature of their business, can operate anywhere but only require money from losing bettors and don’t require the wagered money up front, creating the possibility of debt to the bookie from the bettor. This creates a number of other criminal elements, thus furthering their illegality.
Sports betting has resulted in a number of scandals in sport, affecting the integrity of sports events through various acts including point shaving (players affecting the score by missing shots), spot-fixing (a player action is fixed), bad calls from officials at key moments, and overall match fixing (the overall result of the event is fixed). Examples include the 1919 World Series, the alleged (and later admitted) illegal gambling of former MLB player Pete Rose, and former NBA referee Tim Donaghy. One of the biggest scandals of all involves the 2002 NBA Championship games. Tim Donaghy was allegedly gambling on the spreads for the games that he refereed. After his trial, Tim Donaghy went on to release a statement to the public saying how one of the most controversial games in NBA history, Game six of the 2002 NBA Western Conference finals, was rigged.
In the United States
For example, before game 5 of the 2012 NBA Finals, the Miami Heat were expected to beat the Oklahoma City Thunder. The line read: Miami −3.5, Oklahoma City +3.5. To determine who wins against the spread, the line is either added or subtracted from a team’s final score.
Moneyline bets do not have a spread or handicap, and require the chosen team to win the game outright. The favoured team pays lower odds than does the underdog, thus, it acts mainly as an enticement to take the underdog for a better payout. Sometimes a bettor may couple this type of bet on the favored team to increase the payout of a parlay.
- Spread betting are wagers that are made against the spread. The spread, or line, is a number assigned by the bookmakers which handicaps one team and favors another when two teams play each other and one is perceived as being more likely to win. The favorite “takes” points from the final score and the underdog “gives” points. This number can also be in increments of half-a-point (.5) even though very few sports have .5 point scoring (i.e., The Ryder Cup), in order to avoid the possibility of a tie.
In the above example, if the bettor chose Miami, he would subtract 4 points from Miami’s final score and compare that to Oklahoma City’s final score. If taking Oklahoma City, he will add 3 points to Oklahoma City’s final score.
For him to win his bet, Miami would have to win the game by 4 points or more.
And if a bettor took Oklahoma City, they would have to win outright or lose by 3 or less points.
If the final adjusted score is a tie, the bet is considered a push. The half point at the end is sometimes added to eliminate the possibility of a push. This is the most common type of bet in American sports betting.
- Total (Over/Under) bets are wagers made based on the total score between both teams. Example, if an MLB game has a total of 10.5, an over bettor will want the combined total to be greater, and the opposite for a bettor taking the under. If the combined total is the same as the proposed total, the bet is a push. Most sportsbooks refund all wagers on pushes, though a minority counts them as losses.
- Proposition bets are wagers made on a very specific outcome of a match not related to the final score, usually of a statistical nature. Examples include predicting the number of goals a star player scores in an association football match, betting whether a player will run for a certain number of yards in an American football game, or wagering that a baseball player on one team will accumulate more hits than another player on the opposing team.
- Parlays. A parlay involves multiple bets that rewards successful bettors with a greater payout only if all bets in the parlay win. A parlay is at least two bets, but can be as many as the bookmaker will allow.
The possible payout of the parlay is determined by the combined likelihood of all bets placed. A parlay of riskier bets (more underdogs) will pay greater than a parlay of more likely bets (more favorites). In a parlay, all bets need to win in order for the parlay to win. If one of the bets on a parlay loses, the whole parlay loses. In the event of a push, the pushed bet would be taken out of the parlay and the parlay would bump down to a set of odds without that bet.
Parlays are very appealing to bettors because they pay out much more than the total winnings of their constituent straight bets. However, it is much more difficult to hit on a parlay than it is on a single wager.
- Teasers. A teaser is a parlay that gives the bettor an advantage at a lower, but still positive, payout if successful.
The bettor selects the sport(s), number of games, and number of points given.
If the bettor takes two NBA games at +6.5 it will adjust the individual bets at that rate. So a bet on a 3-point underdog at +3 will become a bet at +9.5 points, and for favorites, it will change a 3-point favorite at −3 to +3.5 points.
Although the rules to win his bet are the same as a parlay, he is paid less than a regular parlay due to the increased odds of winning.
- If bets. An if bet consists of at least two straight bets joined together by an if clause which determines the wager process. If the player’s first selection complies with the condition (clause), then the second selection will have action; if the second selection complies with the condition, then the third selection will have action and so on.
- Run line, puck line, or goal line bets. These are wagers offered as alternatives to moneyline wagers in baseball, hockey, or soccer, respectively. These bets are effectively point spread bets that have the same moneyline odds on either side of the wager (i.e. industry standard of -110 to -115). Sportsbooks will occasionally shift the moneyline by a few points on either side of these spread bets.
- Futures wagers. While all sports wagers are by definition on future events, bets listed as “futures” generally have a long-term horizon measured in weeks or months; for example, a bet that a certain NFL team will win the Super Bowl for the upcoming season. Such a bet can be made before the season starts in September for the best possible payout, but futures are typically available year-round, with payouts being reduced as the season progresses and it becomes easier to predict a champion. In this example, winning bets will not pay off until the conclusion of the Super Bowl in January or February (although many of the losing bets will be clear well before then and can be closed out by the book). Odds for such a bet generally are expressed in a ratio of units paid to unit wagered. The team wagered upon might be 50–1 (or +5000) to win the Super Bowl, which means that the bet will pay 50 times the amount wagered if the team does so. In general, most sportsbooks will prefer this type of wager due to the low win-probability, and also the longer period of time in which the house holds the player’s money while the bet is pending. For this same reason, most professional bettors do not prefer to place futures bets.
A sportsbook may choose to buy in-play futures wagers at a price below the actual payout before a championship is decided if the potential payout is very high (and thus, damaging to the sportsbook due to the money that may be lost). The most recent example of this was when Leicester City pursued and went on to win the 2015/16 Premier League.
- Head-to-Head. In these bets, bettor predicts competitors results against each other and not on the overall result of the event. One example are Formula One races, where you bet on two or three drivers and their placement among the others. Sometimes you can also bet a “tie”, in which one or both drivers either have the same time, drop out, or get disqualified.
- Totalizators. In totalizators (sometimes called flexible-rate bets) the odds are changing in real-time according to the share of total exchange each of the possible outcomes have received taking into account the return rate of the bookmaker offering the bet. For example: If the bookmakers return percentage is 90%, 90% of the amount placed on the winning result will be given back to bettors and 10% goes to the bookmaker. Naturally the more money bet on a certain result, the smaller the odds on that outcome become. This is similar to parimutuel wagering in horse racing and dog racing.
- Half bets. A half (halftime) bet applies only to the score of the first or second half. This bet can be placed on the spread (line) or over/under. This can also be applied to a specific quarter in American football or basketball, a fewer number of innings in baseball, or a specific period in hockey.
- In-play betting. In-play betting, or live betting, is a fairly new feature offered by some online sports books that enables bettors to place new bets while a sporting event is in progress. In-play betting first appeared towards the end of the 1990s when some bookmakers would take bets over the telephone whilst a sports event was in progress, and has now evolved into a popular online service in many countries. The introduction of in-play betting has allowed bookmakers to increase the number of markets available to bet on during sports events, and gamblers are able to place bets based on many different types of in-game activity during the matches. For example, in football matches, it is possible to bet in on in-play markets including the match result, half-time score, number of goals scored in the first or second half of the game, the number of yellow cards during the match, and the name of the goal scorers.  The availability of a particular sport and in-play markets varies from bookmaker to bookmaker. In-play sports betting has structural characteristics that have changed the mechanics of gambling for sports bettors, as they are now able to place a larger number of bets during a single sports game (as opposed to a single bet on who is going to win). One of the most important differences between being able to place an in-running sports bet opposed to a pre-match bet is that the nature of the market has been turned what was previously a discontinuous form of gambling into a continuous one. The gambling study literature has suggested that in-play sports betting may offer more of a risk to problem gamblers because it allows the option for high-speed continuous betting and requires rapid and impulsive decisions in the absence of time for reflection. There are three different types of in-play sports betting products(cash out, Edit my Acca, and Edit my Bet).
- Cash Out. Cash Out betting functionality lets the user of a betting website take profit early if their bet is coming in, or get some of their stake back if their bet is going against them—all before the event is over. Cash Out offers are optionally made by the website in real time on some of the current bets held by the user and are optionally taken by the user by clicking on a button on the webpage to “Cash out”. Cash Out sports betting functionality developed on digital betting websites after 2008 with the evolution of betting exchanges. It was later adopted by online sports books and suppliers of betting software. ‘Cash out’ is offered to users by online sportsbook operators based on the profitability of offering the option to the user to divest their existing bet on an outcome and is sometimes available on singles and multiples. It is regularly offered on a wide range of sports, including American football, tennis, horse racing, basketball, and most other markets. You can Cash Out of bets pre-play, in-play, and between legs, prior to the outcome of the event. It has proved a key customer retention tool for sports book operators looking to capitalize on the use of mobile handsets while the bettor/user is also watching a given event.
- Edit My Acca. This feature allows gamblers to remove selections from their accumulator after the bet has been placed and in some instances after the selected event has started. The betting slip is then revised to feature the amended selections and a new potential return amount. This can be done online or via a mobile device.
- Edit My Bet. The ‘edit bet’ feature can be used by gamblers to ‘unsettle straight accumulators’ before matches have started or whilst they are in-play. The feature can also be used for to swap single bets for new bets, and the gambler is given a new bet selection valued at the bookie’s cash out price to reflect live market/game odds for the original bet.
The bookmaker functions as a market maker for sports wagers, most of which have a binary outcome: a team either wins or loses. The bookmaker accepts both wagers, and maintains a spread (the vigorish) which will ensure a profit regardless of the outcome of the wager. The Federal Wire Act of 1961 was an attempt by the US government to prevent illegal bookmaking. However, this Act does not apply to other types of online gambling. The Supreme Court has not ruled on the meaning of the Federal Wire Act as it pertains to online gambling.
Bookmakers usually hold an 11–10 advantage over their customers—for small wagers it is closer to a 6–5 advantage—so the bookmaker will most likely survive over the long term. Successful bookmakers must be able to withstand a large short term loss. (Boyd, 1981)
Many of the leading gambling bookmakers from the 1930s to the 1960s got their start during the prohibition era of the 1920s. They were often descendants of the influx of immigrants coming into the USA at this time. Although the common stereotype is that these bookies were of Italian descent, many leading bookies were of eastern European ancestry.
Odds for different outcomes in single bet are presented either in European format (decimal odds), UK format (fractional odds), or American format (moneyline odds). European format (decimal odds) are used in continental Europe, Canada, and Australia. They are the ratio of the full payout to the stake, in a decimal format. Decimal odds of 2.00 are an even bet. UK format (fractional odds) are used by British bookmakers. They are the ratio of the amount won to the stake – the solidus “/” is pronounced “to” for example 7/1 “seven to one”. Fractional odds of 1/1 are an even bet. US format odds are the amount won on a 100 stake when positive and the stake needed to win 100 when negative. US odds of 100 are an even bet.