The gap concept in No Limit Hold'em
What is the gap concept?
You may have heard this expression before, as it is part of the poker tournament lingo. It was first coined by David Sklansky, one of the most famous gambling and in particular poker theorists.
In short, the gap concept says that you must have a tighter range when you call a raise pre flop then the range you would use to raise yourself if first to act. The difference between these two ranges is the gap, i.e. how stronger your hand shoud be.
The gap concept in practice.
An example will best clarify the gap concept. You have AJs in middle position at a Full Tilt tournament. If a tight player raises 4BB from the cutoff and everyone folds to you, the standard move is to fold, as your hand is likely dominated (for example by {AKs, QQ+}).
On the contrary if you are first to act from the same middle position with the same cards, you should raise yourself this time. Because this hand is strong enough given that a few players have already folded.
This is the simplicity of the gap concept. AJs is too weak to call a raise, but strong enough that you can raise yourself if first to act. This can be confusing to new players, and only practice will teach why the gap concept is such a fundamental truth.
The gap concept explained
Why is there such a gap? Two important concepts associated with the gap concept are the notions of position and aggression in poker.
If you are first to raise from middle position, you have some information: the earlier players have folded and until further notice you have the strongest hand with AJs. You should use aggression to get the pot now or at least thin out the field.
But on the other hand if there is already an early raiser, now you have different information: there is already one player in the hand who is representing strong cards. Therefore, this automatically lowers the value of your hand as you know you must compete to win this pot. This is not the same fight, this is a harder fight, and so you need a better hand than before.
Position comes into play in the gap concept because if there is a raiser earlier than you, he knows that he has a positional disadvantage. Therefore we can assume that he must have a stronger hand that we need ourselves to raise from where we are. Therefore we need a super-strong hand to call him, stronger than if we are first to raise.
Good game at the tables!