Bridge
Opening lead — three of spades. There is no simple rule governing the question of when a defender should cover an honour with an honour. In general, a defender covers when his side may gain a trick by doing so, and does not cover when it might cost him a trick to do so.
Consider this deal where East wins the opening spade lead with the king and returns the five to dummy’s ace. Declarer leads the ten of clubs from dummy, and the question is whether East should cover with the king.
In the given situation, he should. Observe what happens when he doesn’t. The ten wins, and a club continuation gives South four club tricks and the contract. But if East plays the king on the ten, South makes only three club tricks and goes down one, since West’s nine becomes a stopper in the suit.
East has nothing to lose by covering, but stands to gain, depending on declarer’s club holding. If, for example, South has A-Q-9-3, A-J-8-3, QJ-8-3 or his actual holding, the failure to cover costs a trick, while covering gains a trick.
Declarer can sometimes foil the defence by not leading an honour in the first place. Thus, in the present case, once South appreciates the futility of leading the ten because East will play the king if he has it, he should lead the deuce instead.
When the queen wins, South returns to dummy with a heart and again leads a low club (not the ten). As it happens, East is obliged to play the king, and South's worries are over, since he brings home four club tricks and the contract.