There is another case, known as Deschapelles' coup, where the proper card to lead is not determined by the leader's numerical power in the suit. It is this: all the adversaries' and partner's trumps are exhausted, and the leader's partner remains with an established suit. If the leader (not having any of his partner's suit left) is obliged to open a fresh suit headed by king, queen, or knave, he should lead the highest card, irrespective of the number of cards he holds in the suit, that being the best chance of subsequently procuring the lead for his partner in case his only card of entry in that suit should be an honour, not the ace.
For an illustration of this coup, see Hand XXVIII.
Deschapelles' coup often succeeds in practice, but it may generally be defeated by an attentive player. When the above-described position of the cards occurs, the adversary, if he has the ace of the fresh suit led, should not put it on first round. The suit will, in all probability, be continued with a low card, when the third player will most likely be compelled to play his highest, which will be taken by the ace; and, having lost the card of re-entry, he never brings in his suit, unless he gets the lead in some other way.
REFUSING TO WIN THE SECOND ROUND OF A SUIT.
This is a case of by no means infrequent occurrence. For example: one of the adversaries has a long suit declared in his favour, which is led a second time. Only one trump remains in, which is in the hand of the second or fourth player. As a rule, the second round of the suit should not be trumped. The third round will probably exhaust the adverse hand, which is numerically weak in the suit. If it so happens that the player who is numerically strong in it has no card of re-entry in any other suit, he will then never bring in his long suit, as his partner, whose hand is exhausted, cannot lead it again, should he get the lead after the third round. If there is a card of re-entry in the hand of the player who has numerical strength, he must bring in the suit, whether the second round is trumped or not.
See Hand XXIX for an illustration of this position.
A similar rule applies, but less frequently, when one adversary has the long trumps, and his partner a long suit nearly established.