When the original lead is a trump, it should be returned in every case, either immediately, or as soon as the player can obtain the lead.
The same reasons for changing suits as those given for the original leader will apply to the Third Hand.
RULES FOR RETURNING PARTNER’S SUITS. When the original leader’s suit is returned by his partner, either immediately or upon his regaining the lead, it is usual to show, if possible, how many cards remain in the Third Hand, so that by adding them to his own, the leader may estimate the number held by his adversaries. This consideration is secondary to the return of the best, or one of the second and third best; but in the absence of such cards, the Third Hand should always return the higher of only two remaining, and the lowest of three or more, regardless of their value.
In addition to the foregoing conventionalities, which are proper to the leader of a suit and his partner, there are two usages which apply equally to any player at the table. These are discarding and forcing.
Discarding. When a player cannot follow suit, and does not wish to trump, his safest play is to discard whatever seems of least use to him. It is not considered good play to unguard a King or to leave an Ace alone; but this may be done if the partner is leading trumps, and there is a good established suit to keep. Beginners should be careful to preserve cards of re-entry, even if they have to discard from their good suit in order to do so.
When the adversaries have shown strength in trumps, or are leading them, there is little use in keeping a long suit together. It is much better to keep guard on the suits in which they are probably strong, letting your own and your partner’s go.
A player having full command of a suit, may show it to his partner by discarding the best card of it. Discarding the second-best is an indication that the player has not the best; and in general, the discard of any small card shows weakness in that suit.
Forcing. We have already observed that a player who is weak himself should not force his partner. An exception may be made in cases where he has shown weakness, or has had a chance to lead trumps and has not done so. On the contrary, an adversary should not be forced unless he has shown strength, or the player forcing him is weak. The hope of a player with a good suit is to defend it by leading and exhausting the trumps. His adversary tries to keep his trumps in order to stop that suit; at the same time forcing the strong hand, by leading cards which he must trump, hoping that such a force may so weaken him that he will be unable to continue the trump lead.
It is usually very difficult to convince the beginner that the weaker he is himself, the more reason he has for forcing the adversaries to trump his good cards. He is constantly falling into the error of changing from a good suit, which the adversaries cannot stop without trumping, to a weak suit, which allows them to get into the lead without any waste of trump strength. If an adversary refuses to trump a suit, it is imperative to keep on with it until he does; for it is always good play to force an adversary to do what he does not wish to do.
Any person may convince himself of the soundness of this theory of forcing, by giving himself the six highest cards in any suit, three small cards in the others, and four trumps; giving another player the four best trumps, and nine of the highest cards in two suits. If the first player forces the second with his good suit, and continues every time he gets the lead, he must win six tricks; if he does not, the second player makes a slam.