As a defender, we sometimes have a secret. We know that declarer is going to ruff something, but we also know that our partner who is sitting behind declarer, might be able to overruff. This particular position seems simple, but has many variations and conflicts. 

 

Here's a basic example: 

Vul: Dlr:	J109  --  43
K765  --  A		AQ32  9
	84  AK  2

The contract is spades. 

If East-West were on lead, they could take the rest of the tricks. However, if SOUTH is on lead, South can play a high heart. If declarer ruffs low, partner can overruff. If declarer ruffs with the K, partner will eventually get a spade trick. Neat. 

 

 

 

 

 

If we move some cards around, though, we can start to see the complexity of this situation: 

 

In this example, one trump has already been played (it doesn't matter who played it). 

Vul: Dlr:	J109  --  43
K765  --  5		AQ2  9  2
	84  AK  A

 

 

 

 

 

 

 

 

What should declarer do if we play a heart? Discard a diamond! Often in these promotion situations, declarer might sense this position coming. Cashing our outside winners first can be key. South needs to play the A first to prevent West from being able to execute this loser substitution

Let's look at a full deal and try to figure out exactly what our best defense is. 

 

Auction: 2 dbl p 2h p 4S ap

 

Vul: EW Dlr:N	J5  65  AJ9842  75
AKQ632  87  K  AKQJ		87  K1094  Q653  972
	1094  AQJ32  107  1086

 

Declarer is known to have a big hand with lots of spades. Partner's 6 might be a singleton or a doubleton. We win the J. Then what? 

 

Take a good look at that dummy. What use will it be to declarer? None at all. There's no reason to expect your heart tricks to go away. If partner has a singleton, that means declarer will always have to lose three hearts to you. You have another inference from the auction. With a big hand and three hearts, declarer might have tried a 3 cuebid over partner's 2 to suggest hearts as a possible suit. 

 

If we rush to give partner a ruff in hearts by playing the A and another, declarer will throw away the one diamond they have and claim on the next trick. Instead, we need to play a diamond now. We're not looking for a ruff, but diamonds are partner's likely entry back into hand. We should probably have a decent guess about what's going on in diamonds. Partner didn't lead the suit so partner probably doesn't have AK. Partner led a side doubleton instead of diamonds, so partner might have the ace and doesn't want to break the suit. This all flows logically. We could almost call out a singleton king before switching. As it happens, West does play the singleton king. Partner wins the ace and continues with a heart. 

Now is it time to win the Q and switch to a club? Again, the dummy has answers for us. If declarer has a club loser: where is it going? However, since dummy has no entries (unless partner preempted on AJ9xx for some reason), there's no risk in cashing the third heart now. You are hoping partner has some honor in spades: even a singleton jack would work. Declarer has to ruff (or go down) and if declarer ruffs with a high honor, your 109 will mature into a trick. Look at the full deal:. 

You can see that if you greedily try to play three rounds of hearts at the beginning, declarer will discard a diamond and you have no recourse. If you switch to a club at trick four, declarer will draw trump in three rounds and claim.