[kgr]

Declarer is in 6S and already lost one trick. From the bidding you know that declarer has a 6-card suit S.
You are sitting East and declarer plays the A from his hand
....Jx
?x....Qxx
....A?????
crosses to dummy and plays the J, you can assume that declarer has the K in his hand:
....J
x....Qx
....K????
Should you cover or not?
- If not: how shoud declarer play with AKxxxx?
- If yes: If the Q does not come over the J should declarer play the K now from AKTxxx (assuming East does not have the Q if not covered, and playing West for Qx)?

[inquiry]

i must be missing the point. There is no need to cover it can never win (the other assumptions being true) so duck is right. If declarer lead the JACK and is missing the queen he has no choice but to let it run, for no matter if Ten is doubleton or Queen is doubleton winning the ace will lose a trick. You have no winning play with Qxx and declarer with AKx has no other play besides duck. Now if declarer has AKT sixth, he might change his mind and play the KING on the second round if you don;t cover.

[jikl]

As Ben said, the ♠ suit in isolation means you should never cover. take these examples:

---

By the way you have asked the question you do not hold the 9 or 10 in your hand so you have no possible winning play by covering the J as the suit is now high. If partner had the 10 it is squashed. There is an argument for playing the Q if you hold the 9, it is possible partner has the 10 but highly unlikely.

Next example:

---

Now you have blown a trick as declarer is VERY likely to rise to drop the Q.

Sean

[HeartA]

There is one exception, that is, if you have 9: Q9x. In that case, if pd has Tx and you didn't cover, you lost a trick.

[kenrexford]

Context must be given to be 100% sure. Assuming that an "x" means a small card that has no potential value, then covering the Jack is almost always wrong. One key exception, however. Suppose Declarer is expected to finesse no matter what, and suppose Declarer had the 10. In that case, one key reason to cover might be transportational. Declarer mighjt, for instance, need two finesses but have no further dummy entires. In this case, your cover gives him a trick he was about to get anyway but deprives him of a needed entry. Another rare justification might remotely be to cater to K10x in partner's hand if you need the entry real quick, or even more remotely a planned jettison under partner's King to avoid an endplay that would cost more than one trick.

Almost no play is 100%.

[pclayton]

If declarer were to play the J immediately, then covering could be right as pard could have 10x and declarer AK9xxx. Once declarer lays down the A, covering can never be right. If declarer has AKTxxx, he's taking the hook anyway, and if AKTxxxx, which is what I think he has, covering is a flat blunder.

By the by, if Declarer has AKxxx; its an interesting swindle to cash the A, and run the Jack. Nice play if you can get away with it.

[kgr]

What if you need 1 more trick to defeat 6S and you have as East:

....Jx
?x....Qxx
....AK????

or

....Jx
?x....Q9x
....AK????

Declarer immediatly plays the J.
Do you cover?

These questions came from a team match where opp was in 6S and already lost a trick. And this was situation in Spades:
....Jx
Qx....xxx
....AKTxxx
(I don't remember who had the 9).
Declarer played the J from dummy and when this was not covered he played the K and A, dropping the Q and making her contract. The argument was that she didn't think East had the Q because he didn't cover the J.

PS: We were defeated by 25-4. Mostly because opps were simply better (at our level this means making less mistakes), but I don't think this was one of the good play...except if it was very good table feel.

[awm]

This is a funny "table feel" sort of thing. The basic point is that we're normally taught to "cover an honor with an honor." So basically:

(1) A beginner will not realize he might be supposed to cover, and will play second hand low in tempo.

(2) An intermediate player will know he should "cover an honor with an honor" and will cover the jack.

(3) An advanced player will think about covering for a bit, realize it can never gain, and then play low... but the break in tempo will be a dead "tell" for a good declarer.

(4) An expert will know not to cover in this situation, and will play second hand low in tempo.

So leading the jack and then taking the ace when it's ducked in tempo will work against intermediate and advanced players to maximize your odds of picking up the suit... but it will be worse than just running the jack against beginners or experts.

Reminds me of a situation from Gerben's blog -- sometimes the beginner and the expert make the same play (but for different reasons) whereas the players in the middle do something else.