This form of trump play is made when there is a 4-4 or 5-4 trump fit (occasionally 5-3) and each hand is short in a different suit.
There are two important features:
1. Cash your winners in side suits before embarking on the crossruff. If you don't do this, there is a danger that one defender (who cannot overruff) will discard your side suits and trump them later.
2. When planning the crossruff, count your winners (rather than normal losers at suit contracts). Sometimes you should count both ways.
North 6 KJ8 853 AT8532
South AQ94 AQT75 K976 void
Contract: 4Opening Lead: 9
Analysis: The 9 lead (passive) suggests that the spade finesse won't succeed. Winners are two aces and five trumps which is only seven tricks. So we must separate the trumps and the only danger is an overruff.
The Play: Win the A discarding a diamond. Trump a club with the 5. Cash the A and ruff a spade with the 8. Next ruff a club with 7. If not overruffed you are home as the rest of the hearts cannot be overruffed. So you now make two aces, five trumps from your hand and three trumps from dummy. That totals ten tricks.
North KQ4 5 Q7432 AQT3
South 862 AKJ62 void KJ876
Contract: 5 Lead:T
Analysis: When dummy came down declarer saw a typical crossruff situation: lots of trumps in both hands and short suits in both hands. Side winners were the AK and nine more tricks were needed. The problem is that five diamonds can be ruffed in hand but only three hearts in dummy. So a spade trick must be established.
The Play: After trumping the opening lead, South should lead a small spade towards dummy. East took the trick with the A and returned a trump. The 6 held, and West showed out. Also East could not overruff dummy's AQT. Declarer now cashed the A and K discarding a small spade, and the cashed the K. Now s/he got the crossruff rolling. Declarer took two hearts, one spade and eight trump tricks for a total of eleven.
There are no absolutes in bridge. Here is an exception:
North 7 KT752 K43 763
South A62 AQ643 92 AK5
Contract: 6 Lead: K
Analysis: There are ten tricks off the top and you have a typical crossruff situation. But you only need to ruff two spades in dummy and two diamonds in hand. Cashing side winners is too dangerous as you cannot risk a ruff.
The Play: Take the A and with ten trumps you can afford to pull all the trumps (even if three are in one hand). Now you go ahead with your crossruff.
North A74 JT87 9 KQ742
South 3 AKQ965 AQ42 85
Contract: 6 Lead: K
Analysis: On hands that look like a crossruff, you first count your winners.
You have eight, plus one by establishing a club trick. You can pick up the extra three tricks by ruffing three diamonds in dummy. But you also need safe entries to your hand as well as establishing clubs and drawing trumps. Correct timing and order of play are vital. If you start off by trumping a spade then leading the A and ruffing a diamond you will end up in dummy with no more spades to lead while you have diamonds in your hand to trump. And you don't want to use up a trump as an entry.
The Play: So don't start trumping spades first. Take the A and lead a diamond to the A and start ruffing diamonds first. The play will go: A, A, 2 ruffed with the 7. Then4 ruffed with the 5, 4 ruffed by the 8, 7 ruffed with the 6 and the Q ruffed by the T. The crossruff is now completed. The J is overtaken with the A and trumps are drawn. Now lose a club and you have twelve tricks.
South AK96 A7543 3 AK5
Contract: 6 Lead:Q
Analysis: The lead indicates length and there is a strong danger that a third heard trumped with the 5 could be overruffed. Can this be avoided?
The Play: Declarer won the first trick in dummy with the K and went to hand with the K. S/he then cashed the A discarding a club. Next s/he cashed the A and ruffed a diamond with the 6. S/he cashed the A and ruffed a club with the 5. Now s/he is home as s/he can continue crossruffing. The only trick s/he can lose is the T.
North QJ84 K942 AK63 6
South AT975 T J42 AT84
Contract: 4 (West opened 1) Lead: K
Analysis: West's opening bid marks him with most of the high cards. The K seems to be a working card. So there are four top tricks and we need six more crossruffing tricks. The trouble is that West will have the K and his spade return will leave you with only two trumps in dummy to ruff three losing clubs.
The Play: South took the A and immediately led a heart. West rose with the A and returned a heart. South discarded the 2. S/he now took the usual precaution of cashing the A and K before anything bad happened. S/he now began the crossruff by trumping a heart with the 5 and a club with the 4. S/he trumped another heart with the 7 and another club with the 8. S/he then trumped a diamond with the 9, but was overruled by the K. But now declarer had eleven tricks!
North A974 AT53 K8 A74
South K2 KJ86 A973 KQ8
Contract: 6 Lead: J
The Play: You should not even try to guess who has the Q. Bang down the A andK. Then go about your business. Cash the clubs, cash the top spades and diamonds then crossruff. Let them have the Q, as you can never take fewer than twelve tricks. Even if the Q falls doubleton, you still need to ruff two spades and two diamonds.