[akhare]

After third hand wins the opening lead against NT, the conventional return is supposed to be the original 4th best holding (assuming you initially held 4 cards in the suit).

Assuming that there are no clues to the length of the suit held by the defenders and that partner's lead shows some interest in the suit lead, what would you return in the following cases ?

a) Dummy is now void in the suit
Dummy has small cards in the suit
c) Dummy has an high winner in the suit, but it's stiff

In a) it might be important to try and prevent declarer from playing low and forcing partner to win. In other words it might be right to play your highest card (assuming you don't hold the length in the suit and the card isn't needed for an entry to your hand).

In c) do you give partner remaining count in the suit?

Also, in case of a) does it matter if you win at trick one or if declarer wins the first trick and you subsequently gain the lead (if you play some echo assume partner signals that he likes the opening suit)?

[bid_em_up]

As a "general" rule, you return small from an original holding of 4, or high from an original holding of 3.

A1052, you win the Ace and return the 2.

A105, you win the Ace and return the 10.

However, there are many times where you may "know" thru the auction or simply suspect that partner has led from a 5 card (or longer) suit. In these cases, depending on your holdings, it may be best to return either the high card or the 2nd highest card to begin to unblock the suit, ie, if you hold A1093, it is like to be necessary to return the 9 or the 10 or the suit may block.

If dummy is void, you should return as high a spot as you can (usually), so partner will not expect another higher card from you.

If dummy's remaining card is a stiff winnner, you should proceed as leading from your original holding (small from 4, high from 3, unblocking from 4 if you think it may be necessary). If your length in partners suit is known (via the auction), the card you return can possibly indicate suit preference, so that partner can win a trick and then put you in for a lead thru declarer (if one is necessary), although this will rarely apply.

Assuming declarers length is known and dummy has one or two small cards remaining in the suit, it is usually best to return a card that beats dummy's holding, if possible.

[whereagles]

This is very advanced stuff. Most textbooks just say "original 4th highest or unsupported honor if the situation calls for it", and leave it to the reader to evaluate the need for 'clever leads' at the table.

There's not much more written about it, though some top pairs probably have some of these discussed.

[SoTired]

normally, return original 4th best whether returning it immediately or later.

but the foremost rule that overrides any other carding rules you have is "Don't signal with a card that potentially may cost a trick."

this means that if partner leads the 2, dummy has 103 and plays the 3 and you have J984. You play the 8 and lose to the Q. Later you get in, you now return the J to smother the 10. It would be silly to let the offense get 2 tricks from KQ5 opposite 103 when declarer guesses right.