Most people believe that bookmakers attempt to “balance” their action, by adjusting their prices so that they get the same amount of money on both sides of a game. Theoretically, the bookmaker’s only financial interest in the bets it accepts is the vigorish it takes from losing wagers, and it simply wants to ensure that the amount of wagers on each side is equal. In reality, however, bookmakers attempt to maximize their bottom line. While having an exactly equal amount of money wagered on each contestant would guarantee themselves a profit and eliminate their risk, that won’t necessarily maximize their bottom line. They can make more money when they accept bets at odds which are “inflated” from those which are likely to occur. So for example, if the majority of their customers are going to bet on a team regardless of the price, they will set the price as high as possible. This is called “shading” the line. Generally, the public prefers to back the favorite, and unsophisticated bettors often show up during large events such as the Final Four and the Super Bowl. Some bookmakers actually offer different prices to different customers, using past bets as an indicator of who the customer will bet on as a way of additionally increasing their potential profit.
With a match offering a point spread, however, bookmakers must be careful of moving the line too much. Assume, for example, that a large number of Oklahoma betters caused the line to be moved from 27 points all the way to 29 points. If Oklahoma won the game by 28 points, the bookmaker would have to pay both those who wagered that Oklahoma would win by 27 and those who took Kansas on the 29 point spread. Bookmakers refer to such an event as “being middled.” This famously occurred in the 1979 Super Bowl between the Pittsburgh Steelers and Dallas Cowboys, which American bookmakers still remember as “Black Sunday.” For that game, bookmakers opened Pittsburgh as a 3.5 point favorite, and the line closed just before kickoff at Pittsburgh -4.5. Pittsburgh won the game 35-31, enabling both those who took the Steelers -3.5 and those who wagered on the Cowboys +4.5 to collect.
Sometimes, a point spread is set at an amount that equals a common margin of victory for a particular sporting event. For instance, American football games are often decided by 3 points (the amount awarded for a field goal) or 7 points (the amount awarded for a touchdown with a successful extra-point attempt). In the case of a football game where the favorite is -7, moving the line up or down would likely result in a middle if the favorite wins by exactly 7 points. In this situation, the bookmaker may choose to adjust the vigorish in response to unbalanced action, rather than move the point spread. If the 7 point favorite is getting the most wagers, a bookmaker may change the vigorish on that team from -7 (-110) to -7 (-120), and move the underdog to +7 (+100). Once this occurs, bettors looking to wager on the favorite must risk $120 for every $100 they wish to win, while underdog players will get even money for every dollar they wager.
A bookmaker’s line can be influenced by one or several large wagers made on a match. Bookmakers pay particular attention to the bets of a professional sports gambler, commonly known within the industry as a “sharp” or “wiseguy.” Some bookmakers will not accept bets from bettors they believe fit in this category. As a result, professionals use “beards” to make the bets for them. Groups of professionals who work together are known as a “syndicate.” These syndicates will often place large wagers with several books simultaneously, causing the prices to move quickly. Observers refer to these fast line movements as “steam.”
Conversely, bettors who are primarily recreational are referred to as “squares”. Online, there are certain betting shops that cater more towards sharps and those toward squares. Shops that cater towards professionals generally have higher (or no) upper betting limits and offer lower vigorish, while making some of the money back on fees for withdrawals or minimum bets. Meanwhile, “square” shops generally have lower betting limits and offer more sigmup bonuses. In return, they charge the standard 11-to-10 vigorish, and offer worse moneylines than the “sharp” shops. In many of the minor sports, sharps make up the majority of bettors, while for large public sporting events such as the NCAA Men’s Division I Basketball Championship and the Super Bowl, recreational bettors make up almost 90% of the betting action at sportsbooks, and are the top betting events both in Nevada and online.
Because of how lines move quickly during sporting events, arbitrage betting is possible. Theoretically, this will guarantee a small profit of 3-6% when a person bets on one line at one shop and on the opposite line at another shop. However, a large sum of capital is required for the amount of reward, and great care must be exercised to avoid accidentally betting on the same side at both shops. Arbitrage situations are commonly found during halftime and intermission periods, where there is a limited amount of time for each bookmaker to determine the line and accept bets.
The Federal Wire Act of 1961 was an attempt by the US government to prevent illegal bookmaking.