Blocker Effects

Hold a card the opponent needs and they can't have it — so their odds of the hand drop. For some hands that's huge; for others it's nothing.

Blockers move frequency, not equity — sometimes by a lot. Hold one card the opponent needs and their odds of the hand can halve; for a straight or a flush, one card barely registers. That asymmetry is why blockers gate the hands you bluff, not the ones you call.

What holding the card does

Each bar is the opponent's chance of holding the hand, shrinking from its base rate as you hold more of the key card. The big number is the drop from your first card.

Hold the matching rank and it caves in

Pocket aces A-A preflop −47%one ace

hold none 2.6%

hold one ace 1.4% −47%

hold two aces 0.5% −81%

Middle set 9-9 on K♦ 9♠ 6♥ −64%one nine

hold none 1.5%

hold one nine 0.5% −64%

hold two nines no combo possible

Trips a king on K♦ K♠ 9♥ −47%one king

hold none 15.8%

hold one king 8.3% −47%

hold two kings you block every copy

Two-card hands shrug off one blocker

The nut straight J-T on Q♦ 9♠ 8♥ −20%one card

hold none 7.2%

one straight card 5.7% −20%

one of each — J-T 4.6% −36%

two of a rank — J-J 4.1% −43%

three of a rank — J-J-J 2.2% −70%

Flush draw 2+ spades on K♠ 9♠ 6♥ −12%one spade

hold none 21.4%

hold one spade 18.7% −12%

hold two spades 16.0% −25%

Made flush 2+ spades on K♠ 9♠ 6♠ −14%one spade

hold none 18.0%

hold one spade 15.5% −14%

hold two spades 12.9% −29%

The nut card is all-or-nothing

The nut-flush card the A♠ on a spade board −100%if you hold it

don't hold it 8.2%

hold it you block every copy

Reading it at the table

Pairs & sets

One matching card halves it; the second can rule it out.
The board-pair card on paired boards gates who keeps barreling for value.

Straights & flushes

They need two specific cards — so one blocker barely moves them.
Stacking a rank bites: J-J blocks the J-T straight harder than J-T does.

The nut card

The bare A♠ removes the hand he most wants to call with — a give-up becomes a bluff.
Any other spade is −12%. That's not a read.

Count first, blocker last

If the value region is already too big at zero blockers, one card won't save the call.
Blockers pick your bluffs, not your bluff-catchers.

The rule underneath: only live copies matter

Every collapse above is the same arithmetic — the opponent's chance of a rank, by how many of its four copies are still unseen. A copy is equally dead on the board or in your hand.

Copies live	PLO4	PLO5	PLO6	vs 4 live · PLO4
4 live — preflopany rank, no cards seen yet (52-card deck)	28.1%	34.1%	39.7%
4 live — floprank absent from K-9-6 (a queen, say)	29.7%	35.9%	41.8%
3 liveone copy gone: the 9 on K-9-6	23.0%	28.1%	33.0%	−23%
2 livetwo gone: the K on K-K-9	15.8%	19.6%	23.2%	−47%
1 livethree gone: the K on K-K-K	8.2%	10.2%	12.2%	−72%

The flop 4-live row (29.7% in PLO4) sits above the preflop 28.1% — a flop that misses a rank crowds out the alternatives, so off-board ranks get slightly more likely (the anti-blocker effect). And the 1-live row is the ceiling for any single "perfect" blocker: even the lone live trip card on a paired board shows up just 8.2% of the time.

Methodology

The opponent's hand is drawn from the deck minus the board minus the named cards you hold. Your other hole cards stay unknown — they remain part of the unseen deck, exactly as in game.
Boards are fixed: K♦9♠6♥ (unpaired), K♦K♠9♥ (paired), K♦K♠K♥ (trips), K♠9♠6♥ (two-tone), K♠9♠6♠ (monotone), Q♦9♠8♥ (nut straight = J-T). All flops, so the opponent draws from 49 unseen cards before your blockers.
Every figure is exact closed-form combinatorics — binomial ratios, zero simulation. "Drop" is p ÷ p₀ − 1 against the 0-held row of the same class.

Unblocked baselines — what a random hand holds on every texture — live at Board & Hand Probabilities. How played ranges bend these numbers: PLO Range Frequencies. What a frequency edge lets you do with sizing: PLO Bet-Sizing Reference.