Watch His Discards!

Q 7 6
A 8 4
K Q 10 5 4 3
9
10 9 K J 8 3
10 J 6 5
A J 9 8 7 2 6
A 10 8 6 Q J 5 4 3
A 5 4 2
K Q 9 7 3 2 Contract: 4 hearts
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K 7 2 Opening lead: 10 of spds, A of dia

This is the hand I chanced on when I decided to see if live people on OKbridge were making the same mistakes my computer did with 4-card suits. This was the second hand I looked at in the most recent tournament, which may or may not be indicative of how common this is. Look at the spade suit. Now what would you say are your chances of making a winner out of the 5? Slim to none? Well, I dunno. Two defenders found two different ways of offering declarer a chance to make a winner out of it, and one did just that, making 4. Anyway, here are the two ways that five became a potential winner.
Opening lead at one table was the 10 of spades, East signalling with the 8! Had declarer ducked the lead, West almost surely would have continued the suit, to be covered by the queen, king and ace in turn. This would have meant that after two spade leads, there were only two cards higher than the five out, and declarer has one of them in dummy! This allows declarer to knock out the jack, and on the fourth round have a winner in the five over the 3! And even without that continuation, declarer can effect the same thing, since West has no choice in what he plays.
This, to be sure, is not a discard but a matter of signalling with too valuable a card. Still, it's in the ballpark of treating your four-card suits with care and noting how your 9's, 8's and even 7's can easily become valuable. However, the next defender did make a careless discard, allowing declarer his contract.
This is a rather amazing hand. Nothing is sitting right for declarer. Even when the opening leader bangs down the ace of diamonds, setting up dummy's K Q, declarer can't really make the contract with good defense. If he draws trump first, ending in dummy, he can't ruff clubs, and those two diamond winners only bring him up to 9 winners. Or if he gets a spade lead, goes to the ace of hearts and leads toward his king of clubs, the ace is in the wrong hand. He seems to get one piece of luck in that West cannot lead a trump now, allowing declarer to ruff two clubs, but there are no diamond winners and those two club-ruff winners wind up being substantially the same as the K Q of diamonds on an ace of diamonds lead.
The king of spades is sitting over the queen amply guarded and there's no 3-3 spade split. I just don't think game can be made except on a defensive error. Which this declarer got.
The opening lead was the ace of diamonds. Declarer ruffed, of course, and chose to take 3 rounds of trump, ending in dummy and take his two diamond winners, sluffing two clubs. East sluffed a club on the king of diamonds and a spade on the queen.
You know, for about an hour, I thought this was going to have to be a case where there was no real clue on what to discard. East properly discards his fifth club on dummy's first diamond honor, keeping two four-carders at that point, and now on the next diamond, he has to play one of them, and I was going to give the example and say substantially, well, if there are no clues here, at least it does show how important that four-card suit is and we'll have to recognize that some choices are harder than others. I feel there is almost always a clue of some sort to guide the defender between two four-carders, but didn't see it here until . . .
I wasn't even looking at the hand. I was downstairs thinking about it when it suddenly struck me: what did declarer sluff on the king of diamonds! Why of course. That should have guided East. Declarer discarded a club, and at that point it's hard to believe that declarer could have started with longer clubs than spades. If he started with three spades or two, wouldn't we expect him to sluff the spades and see what jells with the 4-card (or 5-card) club suit?
Well, it's not certain, of course. I guess we've all seen some strange plays where declarers didn't pursue their best line. But you've gotta attribute some intelligence to your opponents. You can't really count on ineptitude in any specific case. So East has to figure that it's far more likely declarer started with 4 spades than 4 clubs if he's discarding the latter. East must retain his four-card spade suit and follow declarer in sluffing clubs. As it happened, declarer pounced on the error. He led low to his ace of spades, then back to the queen and king, picking up the 10, 9 & 8 on those two tricks. East cashed the jack, his last spade, and declarer now couldn't miss the 5-of-spades winner if he tried -- losing only two spades and a club.
The play where a defender signalled with the 8 was more bizarre than I had remembered. Declarer did win the first round, went to dummy's ace of trump and led a club to the king, taken by West, who now continued spades, declarer playing the queen and East the jack! It was such a bizarre play that one can only presuppose a missed button, but it stood. Declarer now ruffed a diamond, ruffed a club, ruffed a diamond, ruffed a club, cashed the A of hearts, ruffed a diamond to draw trump.
Declarer could have knocked out the K of spades to establish the 5, for an overtrick, much as I said above that he could have knocked out the J, given that incautious signal with the 8, to at least make his contract. But he chose to crossruff out for 10 winners, and so by the time he knocked out the K of spades, East could cash a club winner.