In a top-bracket regional knockout, you wind up on defense against a quiet partscore:
You, West, deal and pass, and South opens 1♦ in fourth seat. You pass, North responds 1♠, and South's 1NT rebid ends the auction.
You lead the ♥3 (fourth-best, standard carding): ♥10, ♥A, ♥5, and partner returns the ♥7: ♥8, ♥9, ♥Q.
Declarer calls for the ♠J, ♠8 (standard count), ♠2, ?
How do you defend?
There might be an argument for winning a deceptive ♠A, but you choose the mundane play of the ♠Q. There doesn't look to be anything better to do than to clear hearts, so you do. Which heart should you return? It probably won't matter, but if you want to give honest suit-preference, you'll return the ♥J. However, partner should be able to work out the position of the ♠A from the play to the first few tricks. Say you return the ♥2. Declarer wins the ♥K and partner discards the ♦4.
Next, declarer leads the ♠K, in this position:
What's your plan?
Based on partner's count signal in spades, you can place declarer with ♠Kxx, so it might seem intuitive to duck, cutting off dummy's spades.
Before you do, though, you should count the tricks. If you win the ♠A, you will have two spades and three hearts. If declarer has both minor-suit aces, the cause is hopeless—declarer has eight tricks. To defeat the contract, you need to find partner with an ace, almost certainly the ♣A, because if declarer has that card, he will have three spade tricks (he can drive out the ♠A and use the ♣K to reach dummy), two hearts, and two clubs. Unless partner passed in third seat with the ♥A and the ♦AK, you won't be able to get to seven tricks before declarer does.
Placing partner with the ♣A, then, the defense can win the race to seven tricks if partner has either the ♣Q or the ♦K as well (the latter is unlikely, for it would mean partner passed ace-king-ace, but disconnected aces and kings is more plausible than an ace-king together with a side ace). In either case, it is correct to win the ♠A now, cash your hearts, and follow partner's signal.
Can ducking cost? That's what West did at the table, and you can see for yourself what happened.
This was the full deal (click NEXT to follow the play):
After the ♠K held, declarer changed tack, reasoning that East rated to have five diamonds based on his first discard. He cashed the ♦A (happy to see the ♦Q fall, but he would not have needed to—see page 5), and played three more rounds of the suit, taking four tricks there, then led a club to the king. East won the ♣A and returned a low club. Knowing that if West held the ♣Q, his hand would be high, declarer rose with the ♣J and took eight tricks.
This isn't a difficult hand in terms of needing to execute any complicated plays or draw any delicate inferences. All it requires is good, solid technique (counting tricks, distribution, and high-cards), making a plan, and staying focused. Still, it's the sort of hand that an expert can get wrong at the table, if they're not "into" the hand. How do I know? Because at the table, West was an expert, and he failed to find the winning play on the second round of spades.
Sidebar: What if West had held a small singleton diamond?
Now after the ♦A drew low cards, declarer would have led a low diamond to the jack and East's queen. A club lead away from the ace would be instantly fatal, so East would have to return a diamond, letting declarer take the marked finesse there. That would put declarer up to six tricks: one spade, two hearts, and three diamonds, so when declarer cashes the last diamond, this is the position:
The defense has taken three tricks (one spade, one heart, one diamond) and appears to have four more winners, but there's a problem. West has to discard down to four cards. If he throws one of his winners, declarer can simply exit with a spade and wait for West to lead away from his ♣Q in the two-card ending. (The location of that card is marked. East has already shown up with the ♥A, ♦Q, and inferentially the ♣A—the ♣Q too would give him an automatic opening hand.) If West keeps all his winners, declarer, with a full count on the hand, simply leads a club toward the king. West's queen pops up, and declarer has seven or eight tricks, depending on the location of the ♣8.
Note that the location of the ♣10 is immaterial here, and declarer has no guesswork, provided that he pays attention to the discards.
Plus... it's free!