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When blackjack was first introduced in the United States it was not very popular, so gambling houses tried offering various bonus payouts to get the players to the tables. One such bonus was a 10-to-1 payout if the player's hand consisted of the ace of spades and a black Jack (either the Jack of clubs or the Jack of spades). This hand was called a "blackjack" and the name stuck to the game even though the bonus payout was soon abolished. As the game is currently played, a "blackjack" may not necessarily contain a jack at all.
Blackjack hands are scored by their point total. The hand with the highest total wins as long as it doesn't exceed 21; a hand with a higher total than 21 is said to bust. Cards 2 through 10 are worth their face value, and face cards (jack, queen, king) are also worth 10. An ace's value is 11 unless this would cause the player to bust, in which case it is worth 1. A hand in which an ace's value is counted as 11 is called a soft hand, because it cannot be busted if the player draws another card.
The goal of each player is to beat the dealer by having the higher, unbusted hand. Note that if the player busts he loses, even if the dealer also busts (therefore Blackjack favors the dealer). If both the player and the dealer have the same point value, it is called a "push", and neither player nor dealer wins the hand. Each player has an independent game with the dealer, so it is possible for the dealer to lose to one player, but still beat the other players in the same round
The minimum bet is printed on a sign on the table and varies from casino to casino, and even table to table. The most common minimum in the U.S. is $5 although these games can be difficult to find on the Strip in Las Vegas, especially on weekends. The Barbary Coast has $3 minimums on weekdays. After initial bets are placed, the dealer deals the cards, either from one or two hand-held decks of cards, known as a "pitch" game, or more commonly from a shoe containing four or more decks. The dealer gives two cards to each player, including himself. One of the dealer's two cards is face-up so all the players can see it, and the other is face down. (The face-down card is known as the "hole card". In European blackjack, the hole card is not actually dealt until the players all play their hands.) The cards are dealt face up from a shoe, or face down if it is a pitch game.

A two-card hand of 21 (an ace plus a ten-value card) is called a "blackjack" or a "natural", and is an automatic winner. A player with a natural is usually paid 3:2 on his bet. In 2003 some casinos started paying only 6:5 on blackjacks; although this reduced payout has generally been restricted to single-deck games where card counting would otherwise be a viable strategy, the move was decried by longtime blackjack players.
The play goes as follows:
If the dealer has blackjack and the player doesn't, the player automatically loses.
If the player has blackjack and the dealer doesn't, the player automatically wins.
If both the player and dealer have blackjack then it's a push.
If neither side has blackjack, then each player plays out his hand, one at a time.
When all the players have finished the dealer plays his hand.
The player's options for playing his or her hand are:
Hit: Take another card.
Stand: Take no more cards.
Double down: Double the wager, take exactly one more card, and then stand.
Split: Double the wager and have each card be the first card in a new hand. This option is available only when both cards have the same value. Sometimes two face cards will be considered acceptable for splitting, as each is 10 points.
Surrender: Forfeit half the bet and give up the hand. Surrender was common during the early- and mid-20th century, but is no longer offered at most casinos.
The player's turn is over after deciding to stand, doubling down to take a single card, or busting. If the player busts, he or she loses the bet even if the dealer goes on to bust.
After all the players have finished making their decisions, the dealer then reveals his or her hidden hole card and plays the hand. House rules say that the dealer must hit until he or she has at least 17, regardless of what the players have. In most casinos a dealer must also hit a soft 17 (such as an ace and a 6). The felt of the table will indicate whether or not the house hits or stands on a soft 17.
If the dealer busts then all remaining players win. Bets are normally paid out at the odds of 1:1.
Some common rules variations include:
one card split aces: a single new card is added to each Ace and the turn ends. They are thus regarded as 11-point cards. No other denomination is subject to this process.
early surrender: player has the option to surrender before dealer checks for Blackjack.
late surrender: player has the option to surrender after dealer checks for Blackjack.
double-down restrictions: double-down allowed only on certain combinations.
dealer hits a soft seventeen (ace-six, which can play as seven or seventeen)
European No-Hole-Card Rule: the dealer receives only one card, dealt face-up, and does not receive a second card (and thus does not check for blackjack) until players have acted. This means players lose not only their original bet, but also any additional money invested from splitting and doubling down. A game that has no-hole-card doesn't necessarily mean you will lose additional bets as well as original bets. In Australia for example, a player beaten by a dealer blackjack may keep all split and double bets and lose only the original bet, thus the game plays the same as it would if there were a hole card.
There are more than a few blackjack variations which can be found in the casinos, each has its own set of rules, strategies and odds. It is advised to take a look at the rules of the specific variation before playing.
In the United Kingdom, for example, the rules of a legal game in a licensed casino are established by The Gaming Clubs (Bankers' Games) Regulations 1994 (Statutory Instrument 1994/2899), as later amended by S.I. 2000/597 and S.I. 2002/1130. The amendment effective 1 April 2000 allows the game to be played by a single player playing only one hand; previously, a game had to involve (in addition to the banker) more than one person, or one person playing more than one hand. The amendment effective 13 May 2002 allowed, for the first time, the banker to draw on a "soft" 17. The rules specify that the cards must be dealt from a shoe containing either four or six packs of cards. The odds payable for a blackjack must be 3 to 2. A player can take insurance (see below) at odds of 2 to 1, if the dealer has a blackjack. A player can double down, but only on an initial score of 9, 10 or 11. A split is allowed (unless the two cards score 8, 10 or 20) but only one further card is allowed in the case of split aces. The casino is allowed to offer "Under 13" or "Over 13" side wagers, based on the value of the first two cards; for that purpose, an ace has the value 1. The "Under 13" wager must be at odds of 1 to 1 except in the case of two aces, which must pay out at 7 to 1. The "Over 13" wager must be at odds of 1 to 1.