What card removal means
Card removal means the cards in your hand remove certain combinations from your opponent's range.
If you hold an Ace, your opponent has fewer possible Ace-high combinations. If you hold cards that could be part of a draw, your opponent has fewer possible draws.
The effect of having cards in your hand alters the opponent's range and can change the EV of certain actions.
What makes a blocker relevant
A blocker matters only when it changes the strategic range in a meaningful way. For example, if you possess A6 on the board K9425, your A is a relevant blocker because it completely eliminates the nut flush from your opponent's range. This hand is a strong candidate for a bluff because it blocks the opponent's calls.
Another example is if you bet flop and turn with a flush draw and arrived at the river and the flush did not complete. You should be careful about firing a third bet as a bluff, as many of the hands you are hoping your opponent folds – missed flush draws – are blocked by your own missed flush draw. Perhaps a different hand would make a better river bluff.
Using blockers to make a call
A blocker can also make a hand a better bluff-catcher. If you suspect your opponent is often semi-bluffing earlier streets with open-ended straight draws and all straight draws missed, you would be better off calling their river bet if you do not hold a card that blocks their missed straight draws.
For example, if this hypothetical opponent triple-barreled on the board KT548 you would rather call the river bet with K7 than KJ since the first hand unblocks their QJo/QJs bluffs. Not only that, but K7 also blocks their 76s/76o value hands, which removes value hands from their betting range.
The truth about blockers
Blocker effects show up all the time in the solver, because the solver's goal is absolute perfection and every detail matters. In practice, many situations are more impacted by player-specific tendencies and exploits than anything else.
If a player is vastly overcalling, we should not be bluffing regardless of whether we have good blockers or not. If a player is folding too much, we can and should be betting some of our bluffs with less-than-ideal blockers. Blockers are a tool to help us make better decisions, particular in close spots, but they are not a substitute for common sense.
Common blocker mistakes
Beginners often:
- completely ignore blocker effects even in easily applicable spots
- use blockers as a crutch to justify bad bluffs or calls against specific opponents
- overvalue blockers in situations in spots where they are not relevant
A common example of misapplying blockers is on paired flush boards such as T9973. If we bluff-raise all-in with a hand like T7 because we "block full houses", but our opponent will call off with any three-of-a-kind, straight, or flush, we are going to be losing a lot of chips in the long run. The blocker effect is real, but we must be careful about when it makes sense to consider and when it does not.
Key takeaways
Blockers always affect ranges, but they are not always important to consider. A blocker is only relevant when it changes the opponent's range in a way that meaningfully affects the EV of our actions.