Knockout squeeze

A positional squeeze can entail an entry-shift, and in fact the squeeze given above is positional — it will not operate if the East-West hands are switched. But many knockout squeezes are not positional but automatic — that is, the threats are located such that the squeeze operates against either opponent. Here is an example:

With spades trump, North has the lead. South needs three of the last five tricks. He leads dummy's club to knockout-squeeze East. If East discards a trump, South will be able to take two trumps in his hand and ruff a diamond in dummy. If East discards anything else, South ruffs low and leads a diamond, to win two trumps and a red suit trick, or two trumps and a diamond ruff, depending on how East defends.

The ruff of the ♣8 in South's hand still operates a squeeze if the East-West hands are switched, so the position is an automatic squeeze:

South ruffs the ♣8 with the ♠8, and West is backwash-squeezed. The threats are the same as in the prior case, where East is squeezed. But the position is characteristic of a backwash squeeze: West is squeezed in three suits; one of the threats is against West's ability to lead trump effectively; there is no structural two-card menace consisting of an entry and a threat card; West is squeezed as South ruffs a card in the fourth suit.

Discussing the relationship between backwash and knockout squeezes, Ottlik and Kelsey^[2] state, "The KO [knockout] squeeze is, in fact, the general form of the strategic squeeze against 'idle' trump cards, of which the backwash . . . is a particular case."

The backwash and the knockout squeezes can be distinguished by whether the squeezed defender must play before or after third hand ruffs: in the knockout squeeze, the squeezed defender plays prior to the ruff; in the backwash squeeze, after. The following example is from Ottlik and Kelsey:

Against 4♠, West leads a small trump. The defense is now a tempo ahead, if South plays to ruff a diamond in dummy. Seeing this, South wins dummy's ♠8, takes the heart finesse, and cashes the ♣K, the ♣A, and then ruffs the ♣8 with the ♠K in this position:

East is knockout-squeezed. On the ♣8:

But suppose that the East-West hands are switched, except that East retains the ♥K (the successful heart finesse plays no role in the squeeze itself):

South plays as before, winning the trump opening lead in dummy, taking the heart finesse, and then playing on clubs, to reach this position before leading the third club:

South ruffs the third round of clubs with the ♠K and West is backwash-squeezed. The defense has the same losing options as it does when East is knockout-squeezed. Regardless of the terminology, this matrix of threats results in an automatic squeeze.