This hand came up in the Chicago Winter Sectional. The scoring is IMPS, and nobody is vulnerable.
West East
76 S QJT532
A9742 H Q5
A6 D Q5
K964 C AT7
West dealt and opened one heart; North passed, East bid one spade, and
South passed. West rebid two clubs, and East passed. East-West were
playing a convention called "fourth-suit-forcing-to-game" in which a bid
of two diamonds here (the fourth suit) is artificial and game forcing.
As a consequence, all other rebids by East were non-forcing, so East chose
to bid three spades, which was invitational. However, West apparently
forgot that three spades was invitational; he chose to bid four spades when
he should have passed.
This contract looks very grim! If the spades break 3-2 (which happens about two-thirds of the time), then E-W will take four spades; in addition, there are four other "top tricks" -- the red aces and the ace-king of clubs.
South led the queen of clubs. In standard methods, South is either short in clubs or has the jack as well as the queen; because of this, you'd want to win the ace of clubs, retaining the king-nine over South's jack for a later finesse. However, North-South were playing a convention called "Rusinow leads", in which the lead of the queen shows either shortness or the *king*. Since West has the king, it follows that South led from shortness, and hence that North probably has the jack. Therefore East must win the first trick with the king, retaining a finesse position over North's jack.
The club finesse, when taken later on, will provide declarer with a 9th trick -- unless South ruffs a club first, of course. To obtain a 10th trick, East must hope that North started with the red kings. What East would like to do is this; draw trump, then play a diamond to the ace, and play a low heart away from the ace and toward the queen. If North plays low, then East will play the queen; if the queen wins, then East now has 10 tricks. However, if North rises with the heart king, he can now cash the diamond king to defeat the contract. But even if he wins the heart king and doesn't play the diamond king, East still loses, for it is impossible to take both the heart queen and the heart ace separately -- East needs an additional dummy entry.
When I played this contract, I was offered an additional chance -- but I wasn't able to take advantage of it. I won the club king on trick one, then played a trump to South's ace. South then played a trump to North's king, and North played a low club. I held ace-ten in hand, and the board had nine-six-four. I couldn't help but win the club in my hand, and so I was short a dummy entry. Down one.
However, suppose that when I won the king of clubs on trick one, I had discarded the *ten* of clubs from my hand instead of the seven. If North defends the same way, then on the low club lead on trick four I can play the seven from my hand and win on the board with the nine of clubs. I can then play a low heart toward my queen, retaining the diamond ace as a later dummy entry so that I can cash the good heart honors separately. This gives chances for ten tricks even if North correctly rises with the heart king.
The flaw with discarding the club ten on trick one is that it eliminates my ability to take the marked finesse of North for the club jack -- I have to hope that North plays clubs for me. You see, if I play a low club from dummy towards my ace-seven, North can insert the eight, and later score his jack. So while discarding the ten gives possibilities for ten tricks, it also makes it more likely that you'll go down two instead of down one. At IMP scoring, where making the contract is the most important thing, the risk of going down two is often worth it if it gains a possibility of making the contract. This is not true at matchpoint scoring.
As a final observation, note that if East's clubs were ace-ten-eight and not ace-ten-seven, then discarding the ten on trick one would not hurt; in fact, it would be an automatic expert play -- an example of what is called "interior unblocking".