If you watched the World Series you undoubtedly noticed a very common baseball occurrence: the pitcher firmly shaking off the catcher's signal. This takes a certain amount of courage, for a whole stadiumful of people—not to mention a few million TV viewers—is now aware that whatever happens on the next pitch is solely the responsibility of the opinionated man on the mound.
A similar bravery is demanded of the bridge player who, defending a hand, crashes on through his partner's vehement stop signs or ignores his partner's urgent call to continue playing the suit that has been led. He had better be right in his decision or he will lose a lot of points, considerable face and maybe even a partner.
In the following hand West was firmly warned that he could not successfully cash a third trick in clubs. But West knew something about the hand which his partner did not.
South is a full trick short of the textbook requirement for a vulnerable preemptive bid. The rule of two and three—that you may overbid by two tricks when vulnerable and three tricks not vulnerable—is based on the sensible precaution that you should not risk a set of more than 500 points against the opponents' possible game. But nowadays an opening three bid has come to be based upon such flimsy stuff that South, with his 100 honors to hold his losses to no more than 700 if partner were trickless, was not wildly out of line when he chose to open with four hearts.
West had to exercise restraint to keep from doubling. But his partner had already passed, so hopes of an East-West game were slight and if South happened to hold a singleton or void in clubs, a double would be very costly.
East played the 4 on his partner's opening lead of the club king and continued with the 6 when West cashed the club queen. West could, therefore, be certain that East had another club and that South was out, for if East had started with only two clubs he would have played high-low. There was a fair chance that East would welcome a switch to diamonds and West had his fingers on the diamond 10 when he paused for a moment to count South's probable hand. South must have had at least seven hearts and very likely the ace of spades as well. (The king-queen of diamonds was a possibility but less likely to warrant an opening four bid.)
So West ignored his partner's signal and played the ace of clubs. South ruffed as expected. But when declarer led a heart, West stepped in-with the ace and led a fourth club, effectively killing dummy's jack before South could use it for a discard. South still had to lose a spade and was set.
West's defense had foreseen the possibility of a squeeze that would have been inescapable if he had shifted to diamonds. Declarer would have won dummy's diamond ace and knocked out the ace of trumps. Then he would ruff the diamond continuation and lead out all his trumps. Forced to hold the high club, West would have to unguard his queen-jack of spades and declarer would win the last three tricks.
Signals are of the utmost value in telling partner your strength and distribution. But it is up to him to make the most effective use of the information.