This deal came up last weekend ago in a match. Opponents bid 1S (11-16 5+suit) - 4S and partner leads the K of diamonds (Rusinow; promising the A). You see this:
What diamond to you play?
Many players would now encourage the lead, especially since they don't want a shift to another suit with this holding. Against suit contracts, the standard expert practise when holding Qxx over dummy's Jxxx after partner leads high showing A-K combination is to discourage. Encouraging show ability to ruff or suggests a holding that avoids setting up the J in dummy if partner continues.
On this deal, let's say you do discourage and partner shifts to a heart won in dummy. Which heart do you play and why?
This must be a singleton. Partner, if expert, should also recognise the diamond position and wouldn't shift to a heart with this dummy unless hoping for a later ruff. So, play the queen! This shows the queen of diamonds (Qx/Qxx). A low heart indicates a possible entry in clubs (A/K) and a middle heart denies an outside entry. Full deal:
This deal eluded the defence at both tables (East encouraging on the lead twice). I think our teammates should have gotten it right, but not having played that much together, they were on different wave lengths.
Get a working knowledge of 'standard' situations. Or pay up.