All bridge played follows the rules of Contract Bridge, sometimes just called bridge. Once bridge became a popular game, players have been trying to come up with ways to improve their bidding and playing the hand. Some have work, and some have not. The Rule of 11 is one of these new conventions that many players use.
The Rule of 11 is used when the final bid is No Trump (NT). The open lead is usually the 4th best from the defenders hand. By subtracting the value of the lead card from 11, the partner of the opening leader can determine how many cards higher than the card lead are by declarer, dummy and himself, since he knows what he has and can see the dummy hand. Based on this information he can set up his strategy.
|♠KJ973||W N↑ S↓ E||♠A105|
When West leads the ♠7 in the hand below, East applies the Rule of 11. This shows that there are four cards higher than the ♠7 that dummy, declarer and East hold. Since East can see the ♠Q and ♠8 in dummy and the ♠A and ♠10 in his own hand, declarer can have no cards higher than the ♠7. Knowing this, if the dummy covers with the ♠8, East knows he can win the trick cheaply with the ♠10.
Author, Beginning Bridge by the Numbers