🚫 Blockers: how your cards change your opponent's hands
The ace of the suit vs. a flush, aces vs. aces — when a blocker works and when it doesn't · Pro
Blockers in Omaha are a powerful but often overrated tool. One right card completely removes the nuts from your opponent, while an "almost right" one changes almost nothing. This lesson has exact numbers: how an ace in your hand lowers the chance of aces for your opponent, how the ace of the suit zeroes out the nut flush, and why the queen of the same suit is nearly useless.
What a blocker is
A blocker is a card in your hand that your opponent needs for a strong hand. If you have it, your opponent doesn't.
Example: on a K♠9♠4♠7♦2♣ river the nuts is the ace-high spade flush. If you hold the ace of spades, nobody at the table can have the nut flush. The chance that a random opponent has the nut flush is 4.9%. With the ace of spades in your hand — zero.
A blocker doesn't always work
Now for the surprise. If instead of the ace you hold the queen of spades, the chance of your opponent having the nut flush drops only from 4.9% to 4.5%. The queen blocks only "ace + queen of spades" hands, while your opponent makes the nuts with the ace of spades and any other spade.
Even two spades in your hand, Q♠J♠, lower the chance of your opponent having any flush only from 22.6% to 15.1%. A blocker really works when you hold the key card — the one without which there is no nuts.
Aces vs. aces
The same effect preflop. The chance that a random opponent has a pair of aces:
— you have no ace — 3%;
— you have one ace — 1.5%;
— you have two aces — 0.5%.
At a six-handed table at least one of five opponents has aces: 14.9% with no ace in your hand and only 2.7% if you hold aces. That's why an ace in your hand is an argument for a 3-bet and a 4-bet: your opponent less often holds a hand that dominates you.
How to use blockers
River bluffs. A pot-sized bluff pays off if your opponent folds more than 50% of the time (a half-pot bet — more than 33%). The best bluffs are hands that block your opponent's nuts but don't block the hands he'll fold.
Calling a big bet. If you block the nuts, your opponent has it less often — calling is more profitable. If you don't block it and you have the second nuts, be more careful.
The nuts without blockers. A J-T straight on 9♥8♥7♣ without extra jacks and tens — your opponent may have the same straight, and the pot gets split.
In the trainer's tasks blockers are counted exactly: we take all the opponent's hands that make the nuts on the river and see what share of them your cards remove. 0% — you don't block, under half — partially, half or more — strongly.
Practice: 10 rivers where the nuts is a straight or a flush.