Why must players follow suit in contract bridge?
Card editor of the London Field W.H. Whitfeld published this bridge problem in 1885. South is declarer and has the lead with hearts as trump. With a sophisticated finesse, South can win every trick. South begins by leading the ace of diamonds, which, depending on what the opponents discard, opens a possible finesse of North's jack of diamonds. Next, South passes the lead to North with a spade that North trumps. North then leads the last heart, and South discards the 10 of clubs. With the lead of the last trump and then the ace of clubs, the defenders are presented with an insurmountable dilemma. East must hold two diamonds or South takes the last two tricks in the suit by discarding a spade. However, in order to hold on to two diamonds, East must discard the jack of spades, which in turn would force West to hold the queen of spades. Since West also needs the queen of diamonds and the jack of clubs to avoid losing a trick, a discard from any of the three suits will allow South to win all of the remaining tricks by an appropriate discard.
In contract bridge, players are required to follow suit as a fundamental rule of trick play. When a card is led to a trick, every other player in rotation must play a card of that same suit if they have one in their hand.1
This requirement is a defining characteristic of trick-taking games, ensuring that the competition for each trick is structured around the suit originally led. If a player is unable to follow suit because they hold no cards of that suit, they are permitted to play any other card, including a trump card if they choose to do so. A trick is then won by the highest card of the suit led or, if a trump was played, by the highest trump card.21