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Advantage gambling, or advantage play, refers to a practice of using legal ways to gain a mathematical advantage while gambling. The term usually refers to house-banked games, but can also refer to games played against other players, such as poker. Someone who practices advantage gambling is often referred to as an advantage player, or AP.
A skillful or knowledgeable player can gain an advantage at a number of games. Blackjack can usually be beaten with card counting and sometimes with shuffle tracking. Some video poker games can be beaten by the use of a strategy card devised by computer analysis of the game. Some progressive slot machines can eventually have such a high jackpot that they offer a positive return when played. Some online games can be beaten with bonus hunting.
Sports and horse betting
Sports and horse betting can be beaten by placing arbitrage bets, which involve placing bets at different bookmakers who are offering different lines. Many online sports books now offer bonuses like free bets or free money. These bonuses usually come with a stipulation that the bettor place a certain number of bets. For example, a site may offer a bettor $50 free if they deposit $100 and place a total of $1000 in bets. These can reduce the vig taken by the house or even offer the bettor a small advantage.
Another form of advantage can be found by betting the "middle" on a sports event. This situation occurs when two bookmakers are offering different lines on the same event, or if a bettor has placed a bet and the bookmaker changes the line. The bettor simply takes the most favorable lines at each bookmaker, and if the result of the contest is between the numbers, or in the "middle", then the bettor wins both bets.
For example, Bookmaker A lists the Jets to be a 4-point favorite over the Bills. Bookmaker B has the Jets as just a 2-point favorite. The advantage player may bet the Bills +4 with Book A and then the Jets -2 with Book B. If the Jets win by 3, the advantage player collects on both bets. If the Jets win by either 2 or 4, the advantage player collects on one winning bet. And if the Jets win or lose by any other total, the two bets cancel out, leaving the advantage player to pay only the vigorish on the bets. Given typical 10-cent lines, a middle need only win 1 time in 21 to break even, which is a realistic goal - the middle is always a plausible result since it is based on the actual strength of the teams. Middling is an example of line arbitrage.
Betting exchanges offer advantage players a chance to make a larger profit than possible with bookmakers because exchanges charge commission only on the net winnings in a particular betting market. One way to make money on the exchanges is "trading" - in the above example, the Jets might be a favorite decimal odds of 1.90 to defeat the Bills. If a "trader" thinks these odds too long he may bet $1000 on the Jets, and should he prove correct and the odds on the Jets get shorter, "lay off" by laying, say, a $1016 bet against the Jets at 1.87. If the Jets win, he collects $900 on his bet on the Jets and pays out approximately $884 on the bet he laid against the Jets. If the Jets lose, he loses his $1000 stake on the Jets but keeps the $1016 stake on the bet he laid against the Jets. Either way, the "trader" makes a $16 profit and he will pay a commission only on that profit (usually not more than 5% or 80 cents in this example) for a net profit of $15.20 regardless of the result. Of course, if the odds go the wrong way the "trader" may lose money but exchanges do not charge a commission in the event of a net loss.
Poker can offer a long-term advantage to a skilled player because it is played against other players and not against the house. The casino usually takes a rake or a time charge. Whether a poker player can win enough from the game to cover the rake and make a profit depends not only on the player's skill, but on the opposition's lack thereof - the degree of difficulty can vary widely from casino to casino. Tables with relatively easy opposition are referred to as "soft."
There is another advantage to playing poker as opposed to games where play is against the house: since the house has no direct interest in the outcome of a poker game, successful poker players can operate openly without risk of being banned by casinos.
Other ways to gain an advantage
Experts disagree about whether or not an advantage can be gained at some other games. One example is dice control. Authors Stanford Wong and Frank Scoblete believe that by setting and throwing the dice in a certain way players can alter the odds at the game of craps enough to gain an advantage.
"Angle shooting" is another type of advantage play. "Angle shooting" refers to legal but possibly unethical ways to beat casino games. One way to get an advantage at a casino is "hole carding" where a player tries to look at the dealer's hole card in blackjack and then uses that information to play his hand differently. Taking advantage of incorrect payouts is another example of angle shooting. Not correcting an inexperienced dealer who pays 2 to 1 on a blackjack instead of 3 to 2 is an example of taking advantage of an incorrect payout.
Angle shooting may also be undertaken in poker. If, for example, an angle shooter attempts to bluff at the end of a hand, and is called, he may announce his hand as a flush even if it does not qualify. If the calling player throws away his hand, the angle shooter will claim the pot with his non-flush, claiming he made an honest error in announcing his hand. Similarly, angle shooters might hold on to a losing hand, hoping the winning hand will be mucked at showdown due to player or dealer error, and then claim the pot. A simple way to avoid being taken advantage of by angle shooting at poker is always protect one's hand and always let the "cards speak"; that is, turning over one's hand at the showdown for all to see.
Comp hustling can be another form of advantage gambling. Players who play games with a low house advantage can get more than their expected loss in free items from the casino. Many advantage players also take steps to maximize the comps they receive from their play.
Hazards of advantage gambling
Casinos sometimes take measures to thwart players who they believe pose a threat to them, especially card-counters or hole-card players. But some casinos tolerate card-counters who do not bet large amounts, who are not good at counting, or who do not use a large betting spread. Some countermeasures include shuffling more frequently, imposing betting limits, "backing off" the player by asking him not to play blackjack any more, or asking the player to leave the casino. In New Jersey, a player may not be asked to leave a table for counting cards, although the house may still impose betting limits or shuffle sooner. Players caught counting cards or hole-carding ultimately may find themselves listed in the Griffin Book and become unwelcome in most casinos. Video poker and skillful progressive slot players are rarely ejected, but it has happened. They may have their comps reduced or eliminated. Skillful sports bettors may have their betting limits reduced and may not be allowed to take advantage of bonuses at online sports books.
Craps players are often stopped from playing if the dice fail to bounce off the back wall of the table.
Advantage players abide by the established rules of the game and thus, in most jurisdictions, are not regarded as committing fraud against the casino. So, while they may face the above casino-imposed sanctions, they are able to operate without the threat of criminal prosecution for their behavior. This is not the case in all jurisdictions however and some advantage players have reported more aggressive countermeasures being taken even in well known gambling locations like Monte Carlo. 
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