An ounce of prevention
Special circumstances sometimes force declarer to abandon the normal way to play a suit. One of the most important reasons for this is to try to prevent a particular defender from gaining the lead.
Take this case where West leads the diamond king against four hearts. When dummy comes down, South sees there are two possible losers in spades, two more in trumps and another in diamonds. If he loses all of them, he goes down two.
On the more positive side, however, declarer notes that he is far more likely to lose one trump trick than two. Furthermore, if everything goes well, he may also be able to discard a loser or two on dummy’s clubs.
The problem for South from the start is to keep the defenders from scoring four tricks before he can take 10. To this end, he must find a way to stop East from gaining the lead and returning a spade through the king.
Accordingly, declarer ducks West’s king of diamonds at trick one to make sure East can’t later win a trick with a diamond. After West exits with a diamond to dummy’s ace, South’s next concern is how to tackle the trumps.
Ordinarily, with this trump combination, declarer might play the ace and another heart. But here, given the circumstances, there is too much danger that East might gain the lead with the king. So at trick three, declarer leads dummy’s trump seven and lets it ride after East plays low.
West wins with the jack but is helpless. Whatever he returns, South picks up East’s king on the next trump lead and easily makes the contract. In fact, if West does not cash his ace of spades after winning the trump jack, declarer finishes with an overtrick.