One of the most subtle arts of bridge is properly assessing the capability of your partner. There are, for example, two kinds of partners and two ways to signal in defensive play. You must match them properly.
The bludgeon method of signaling calls for playing a high card in the suit you want partner to lead. The more delicate method is to play a low card in the suit you don't want partner to lead, leaving it to his good judgment to decide which suit you really do want.
The deal below is an example of the extra profit to be derived from following the delicate method when you are playing with an enlightened partner. But it can be extremely costly to use the right signal with the wrong partner. When you are in doubt about your partner, don't leave him any doubt about what to play. Even if it costs you a trick to use a high card as a signal, it may be cheaper in the long run.
The bidding involved the exercise of considerable judgment. South had seven sure tricks if a spade were led or a safe retreat to two diamonds if opponents bid clubs, so his one no-trump overcall needs no apology. West was barely too weak for a penalty double and did not clutter up the proceedings by what would have been the weakness bid of two hearts. North was too broke even to try to rescue. And East wisely decided that if his partner held a few cards the vulnerable one no-trump contract could be hurt, whereas if West was poverty stricken any further action could lead to calamity.
Had West opened the queen of partner's spade suit, there would have been no story. But West led a low heart, enabling the defenders to collect the first five tricks in that suit. South discarded three spades and was still in a position to run seven tricks if West shifted to partner's suit. But East's first discard was the spade 2. On the last heart East had to decide whether to insure the set by signaling with the 9 of clubs, or simply to tell West not to lead spades by discarding his spade 3 as a follow-up of the 2. East, deciding his partner was too good to need nursemaiding, threw another spade.
Some players, holding the queen of partner's bid suit, might reason that partner threw low spades because he feared declarer held the spade queen. But in this case West realized that a spade lead in the face of partner's loudly negative 2 and 3 would be an insult. West correctly considered it his duty to decide only whether to shift to a club or a diamond. Dummy's length in clubs suggested that South must have based his vulnerable overcall on a long diamond suit. So West shifted to the queen of clubs.
Once again East withheld the club 9, letting the fact that West's queen won the trick speak for itself. When South's jack dropped and West continued by leading the club 3 through dummy's 10, East's carefully hoarded 9-spot became worth an extra 100 points. The result was down three, a penalty of 300 points.
And, of course, if the one no-trump contract had been doubled, South would run to two diamonds—a contract he would make against the likely lead of the spade queen.
By no means am I advocating that a player should usually refuse to lead his partner's suit. Yet it is a good idea to look elsewhere if the opponent's bidding shows he is prepared for that lead.