Hole carding refers to obtaining knowledge of cards that are supposed to be hidden from view in card games. The term is usually applied to blackjack but can apply to other games with hidden hole cards, like three card poker and Caribbean stud poker. So long as it does not involve the use of a device like a mirror or actions like touching the dealer's cards, in most jurisdictions hole carding is a legal form of advantage gambling in casino table games. In other games, like stud poker, casinos normally have rules against rubbernecking or having a confederate stand behind an opponent to signal hole cards.
Blackjack players must usually make playing decisions based on only seeing one of the dealer's cards (the upcard). But if the dealer's hole card is spotted, a player who plays correctly has a theoretical advantage of up to 13% instead of the normal player disadvantage of around 0.5%. A hole-card player will often choose not to make certain plays, such as hitting a hard 19 against a dealer 20, so as not to reveal that he can see the dealer's hole card.
Dealers can thwart this strategy by turning their first card face-up and not dealing their second until the players have all played.
First-basing and spooking
One method of hole carding is to peek at the card when the dealer checks the hole card for blackjack. This is called "first-basing". A modification called "spooking" refers to a partner with a better view peeking at the hole card in the same circumstance and communicating the information to the player. Peeking devices have made these methods largely obsolete.
Front-loading refers to observing the hole card as it is slid under the upcard.  Newer methods of hole-carding concentrate on observation before the down card is placed under the upcard. This provides information about the card even if the dealer upcard is not a ten or an ace. The advantage varies depending on the rules, the percentage of cards seen, and the strategies used.
- Uston, Ken Million Dollar Blackjack. Sept. 1, 1992, Carol Publishing Corporation.