The Gap Concept is a poker theory that applies to both poker tournaments and cash games. It was first introduced by the famous poker author David Sklansky and it is an important concept for every serious poker player.
In short, the Gap Concept states that it requires a stronger hand to call a raise than it does to make a raise yourself. It sounds pretty obvious at first glance but if you take the time to fully understand this concept, it will help your game tremendously.
Let's use an example to explain the Gap Concept:
Let's say you're sitting in a middle position with a hand like ATs. Under normal circumstances, it would be a perfectly acceptable play to open the pot with a raise with this hand. But what if someone in early position makes a raise first? In that case, you probably would not want to call because the hand is too ifffy to play against an early position raiser.
That's a perfect example of the Gap Concept. As you can see, there's a gap between the relative strength of this hand in each circumstance. When raising, we feel perfectly confident with our hand but when facing a raise, we fold that same hand.
The Gap Concept exists because it requires less strength to make a raise than it does to call a raise. When you raise with a hand, you have the advantage of momentum going in to the hand. When you're the raiser, it's easier to get your opponents to fold because you've already shown strength.
On the other side, it takes a stronger hand to call a raise because you lack momentum. You'll have to fight harder to win the pot because your hand looks weaker. In order to get your opponent to fold, you will have to risk more money by making a raise (where he only has to make a bet).
Just as important in the Gap Concept is the issue of position. When an opponent raises first and then it's your turn to act, that usually means the opponent is playing from an earlier position than you. As you should remember from basic poker strategy, people tend to play stronger hands from early position.
If we look back on our example from above, the opponent who raised was in early position. When someone raises from early position, he knows he still has to get past every other person at that table. This early position raiser believes that his hand is stronger than everyone else's hand without even having seen their hands.
Using the Gap Concept
The Gap Concept will eventually become an instinctive part of your poker game. You know that when people raise in front of you, you need to have a stronger hand to call that raise. There are always exceptions to the rule but it's a generally safe rule to follow.
Steal the Blinds
You can also use the Gap Concept from the standpoint as a raiser. When you are playing in late position and the table has folded around to you, you can raise with a wider range of hands.
Because you have the advantage of momentum and are up against fewer hands, you can raise with weaker hands than you could from any other position. The opposite applies to your opponents who have to act from out of position. They will have to have stronger hands to defend their blinds because they do not have the initiative and they're working from out of position.
Defend the Blinds
If you are the person in early position and you suspect someone is using the Gap Concept to steal your blinds, you can counter that by putting in a re-raise yourself. You know that there's a good chance they're rising with a weak hand. So you can represent an even stronger hand by making a re-raise from out of position.
Of course, your opponents will know that sometimes you're just making a defensive play and they'll play back at you with yet another raise. At that point, you'll have to figure out whether or not you are thinking about the same level as your opponent. Sometimes he really will have a strong hand.