What is a straddle?
What is a straddle bet in a cash game?
A straddle bet is when the player under the gun (the player to the left of the big blind) chooses to double the big blind before the cards are dealt. This means that the player after the straddler speaks first in the pre-flop round, and to call, he or she now has to match the amount of the straddle. The straddler gets to act last and has to option to check, call, raise or re-raise, just like the big blind normally does.
However, the player to the left of the straddler has the option to re-straddle by doubling the bet once again, and the player next to him can make another straddle, and so on. The amount of the re-straddle may differ depending on where you play. In some places the re-straddler has to double the total amount the original straddler put in. In others, the re-straddler only needs to double the raise of the original straddler.
The total number of straddles possible depends on how many players are seated at the table, because normally you are not allowed to straddle on the button. Consequently there can, for example, be five straddles in an eight-handed game, three straddles in a six-handed game, and no straddles at all in a three-handed game. (But local rules can also limit the number of straddles to one or two.)
Why do people straddle? The main objective is to "buy the button" and get to act last in the pre-flop round (what you're actually doing is buying the big blind, because the straddle doesn't affect the betting after the flop at all, and you will still be in early position.) Some people straddle just to build the pot and create action at the table.
You can only make straddle bets in cash games. You are not allowed to straddle in tournaments.