Source: Mr Bridge
A crossruff, as its name suggests, is when, as declarer, you alternately trump one suit in dummy, and another in your hand. By these means, you aim to make extra trump tricks.
You are in 4
, on the 
A lead:
A K Q J 10 8 6 4 2 9 7 4 3 |
| 10 9 8 7 8 7 6 4 2 A K 8 2 |
This hand almost plays itself — clearly, you are going to ruff hearts in dummy and diamonds in hand, eventually making all eight trumps and the two top clubs, right? Maybe: the danger is that whilst you are crossruffing the red suits merrily, one of the defenders will discard a club or two. Then when you get around to `cashing’ the club winners, a defender might be able to ruff one of them. These are the East-West hands:
| 6 3 2 A Q J A K 9 7 5 6 5 |
5 4 K 10 9 5 3 Q J 3 Q J 10 |
If you simply ruff the lead and embark on a crossruff, you will fail. When you ruff the fourth round of hearts in dummy, West will discard a club. Thereafter, you will never be able to take your club winners. Can you see how to avoid this sad fate?
You need to cash the top clubs early, preferably leading towards them. Yes, someone might ruff one of the first two clubs (if the suit splits 4-1), but in that case you were surely not going to make the contract. Cashing the side winners early allows you to make the contract whenever it is possible to do so. Even when you know to cash the side winners early, it is still important to play the hand through mentally before you touch a card — seemingly simple hands can have a pitfall or two.
This time, you are in 6, on the K lead:
| A 4 3 2 7 A 6 5 4 K J 10 7 |
| 9 A Q 5 3 2 K 3 2 A Q 9 8 |
Counting your winners, you have four top tricks, and can make all eight trumps on a crossruff. Following the maxim, you cash the side winners first. Did you notice, though, that you must ruff hearts first, or your crossruff will run out of steam? If you collected your four winners ending in dummy, you are going off. If you collected them ending in your hand, you can claim.
So play the A, A, K, A; then crossruff.
Do you think West would have done better to lead a trump? You are right. How should you play on a trump lead? The difference this time is that you can make only seven tricks from the trump suit. It follows that you must risk the heart finesse. Play the K, Q, A-K, A; then crossruff to victory. Taking a finesse is not the same as cashing a winner, but the maxim still applies: you need to do your work in the side suits before you start the crossruff. The maxim that you need to cash side winners early does not mean that you need to cash all of them — cash only those tricks that are necessary for your contract.
You are in 6 on the K lead from West:
| 9 8 7 A K Q 5 A 5 4 3 2 A |
| A K Q J 10 4 3 2 6 5 4 3 2 |
Since West has failed to lead a trump, you can make all eight of your trumps separately. Those eight tricks, plus the minor-suit aces, add up to ten. So it follows that you need to cash two heart tricks immediately, (bringing your total to twelve), before proceeding with the crossruff. Always count your tricks with care before you play a card. If you try to cash a third heart, you may go down if a defender can ruff and return a trump. If, on the other hand, you cash fewer than two hearts, you take the risk that a defender might be able to discard some hearts whilst you are crossruffing in the minors, stopping you from making enough heart tricks. This brings me to my final piece of advice. Notice how much harder these crossruff hands are once the defenders lead trumps. If the auction tells you that declarer will try to crossruff, a trump lead will often be best.