The term cap has two meanings in poker:
A limit to the amount bet or to the number of bets/raises Edit
In physical casinos, there is frequently a house rule that limits the number of bets/raises that can be made on any given betting round, or sometimes, that limits the size of bets or raises in a single round. Typically, caps are only used in limit hold 'em games, but depending on house rules or local statutes, there may be dollar caps for any wagering at all, including poker bets.
Often, a casino will remove the cap from betting rounds when a hand is down to heads up.
Some online casinos now offer "capped" no-limit games. These games do not restrict the size of bets placed rather they cap the amount that can be bet per player for the entire hand. This amount is typically set at 30-40 big blinds but it can vary. When a player reaches the cap in betting for the hand he is treated as being all in regardless of the size of his stack. Should he be called by one or more players the hands will be flipped up and the hand dealt to completion.
To cover one's downcards with a physical paperweight Edit
Placing a marker (often a poker chip, but sometimes a physical token of some kind) on top of one's downcards is called capping' your cards, because you are putting something on top of them (putting a "cap" on their head). This is typically done in games like Hold 'em or Omaha where a player gets a set of initial downcards and will not receive any more.
There are two main reasons for capping one's cards:
- Capping your cards indicates to the dealer that you are intending to play the hand and are not folding. A player with a set of uncapped downcards in front of them may be mistaken as having folded them by a dealer if they are not paying close attention to the action in a game. In particular, if the player is sitting next to the muck, or if the cards are sitting a notable distance in front of the player, close to the middle of the table, it may appear to the dealer that the player has folded (by indicating they are returning the cards to the dealer). If the cards are capped, however, then regardless of where they are, the dealer will not touch the cards, since a cap is a clear indication that a player is still playing their hand. (The only exception to this rule is when a player explicitly tips a dealer by sliding their hand back, facedown, with the tip on top of the hand as though it were still capped; this is only done after the hand is over, so it is clear the player is not folding but is merely returning their hand for shuffling).
- Capping your cards protects your hand in the case of thrown cards or other accidental mucking of cards. If another player flings their hand towards yours and their cards touch yours, your hand is still considered live if your hand was capped. If your hand was not capped, your cards are typically ruled dead if another player's cards touch them at any time for any reason. Vindictive players have been known to intentionally throw their hands into another player's cards solely to kill the other player's hand. As you can imagine, this is easily grounds for banishment from the poker room, and can lead to physical violence.
Because of these two important reasons for capping one's cards, most poker players have gotten into the habit of always capping their cards under all conditions. It's a good habit to get into, because it affords you instant and built-in protection from the two cases outlined above and requires no extra thought once it becomes a habit.
Some players cap their cards the moment they receive them, even before looking at them. Others look first and then cap their cards, hopefully memorizing them first so there will be no need to uncap them during the hand.
An entire small industry of manufacturing tokens for capping hands (often called card covers) has sprung up, with many people using large coins encased in lucite, or lucky charms of one form or another. The majority of small limit players, however, simply use a chip from their chipstack to cap their cards.