Which Card Do You Play?
You are east playing with a new partner in an IMP match and the opponents are not vulnerable. The bidding has gone: South 1NT (11-14): West pass: North 2NT: all pass. Your partner leads the King of clubs (assume he has KQx, his most likely holding).
North (dummy) tables ♠ : KJ ♥ : QJ10 ♦ : QJ1083 ♣ : J104
East (you) hold ♠ : AQ109 ♥ : K63 ♦ : 765 ♣ : A972
Declarer plays the 4 of clubs. Which club do you play?
There is no clearly correct answer to this question without a firm partnership agreement, which you don’t have. If you play the 9 or 7, partner may read this as encouraging (especially since you are marked with the Ace when he holds the first trick) and continue with the Queen. If you play the 2, partner may play you for five clubs since many players play it this way, and again continue with the Queen.
Now, when you play your highest remaining club (other than the Ace) on his Queen, partner may read this as a suit preference for spades and shift. If so, you will collect +150 on the deal. But, on the other hand, partner (who can have at most an additional Jack based on the bidding) can’t be positive that your card is a suit preference since you may have started with only three clubs, and he may reason as follows:
Partner must have at least one outside Ace or the contract can’t be set unless declarer has specifically Ax of diamonds, at most four hearts, and a spade holding weaker than 10xx (or 10xx or 10xxx and he guesses wrong). If partner has four clubs and two outside Aces or five clubs and one outside Ace, then if I continue clubs he will cash out and set the contract. On the other hand, if I switch to a spade and his only outside Ace is the diamond Ace or the heart Ace then (barring declarer’s unlikely holding mentioned above) we won’t set the contract unless he holds five clubs (in which case we will also set it if I continue clubs). Furthermore, if he does hold the spade Ace, but not the Queen, I only break even (unless he started with Ax of clubs, in which case I must switch to have any chance to set the contract).
So, partner has a dilemma and may go wrong. If so, declarer will make and you will be -120 on the deal. I recommend that you eliminate partner’s dilemma. How?
Overtake his lead of the club King with your Ace and return the 9! If you do this, partner is forced to shift. Not only does your 9 suggest a spade switch but, looking at the dummy, nothing else makes any sense. So, you will collect +50. True, you have cost your side two tricks or 100 points if partner would have guessed right without this play. But if he doesn’t, then you will have cost your side 220 points. At IMP’s, the raw score difference between +50 (two IMP’s) and +150 (four IMP’s) is two IMP’s whereas the raw score difference between +50 and -170 (five IMP’s) is seven IMP’s. However, the actual cost to your side will depend upon the result at the other table (among other possible scenarios, if your teammates play a strong 1NT opener they may get to 3NT from the North side and make with a heart lead).
Personally, I think the odds that partner (even if an expert) will switch unless forced to do so are less than even money, in which case you are taking much the worst of it in any scenario. But then, you know your partner better than I do!