The Gap Concept is perhaps the most important pre-flop concept that exists in poker. Despite its importance, many poker players do not even know it exists, yet they still abide by its rules (some players more than others do). If players did not abide by the rules of this concept, they simply would lose there stacks almost immediately. This concept was coined by the great poker theorist David Sklansky in his book Tournament Poker for Advanced Players.
If a player is thinking of entering a pot that has already been opened, that player needs a stronger hand to call the raise than he would need to be the original raiser. The difference between the raising standards and calling standards is known as the gap. This, plain and simple, is the Gap Concept.
For example, suppose a player just got the latest pokerstars download and is holding A9s was in middle position. If all players folded around to the player holding A9s, it is very reasonable for that player to raise the pot. However, now imagine that not all players to act before him folded. Imagine that the player in the UTG+2 position raised. Now, not only should the player with A9s not reraise, he should not even call. A9s should fold. In fact, in this spot, the minimum the player would need to call would be AQ. The distance between the minimum hand the player would need to be the opening raiser and the caller is known as the “Gap”.
The Logic Behind the Concept
There are two main points that outline the logic behind this concept.
1) Part of the reason a player does not need a premium hand to open a pot is the fact that all players may fold to his raise, and he may steal the blinds without a fight. However, a when a player open the pot before him, that advantage is gone.
2) The pokerstars.com player who opened the pot could have been raising with the minimum hand requirement he would have needed to raise or he could have been raising with Aces. The point is, if a player calls a raise with the minimum hand requirement he would have needed to raise, he is probably entering the pot as a big underdog.
This concept explains the reason why a single raise wins many pots in tournament poker. It is because once a player opens the pot, the quality of hands all the other players need to call or reraise goes up dramatically. They may not even know it, but they are abiding by the Gap Concept.