A defensive problem from a Crockford's Plate match.
You lead the heart four declarer plays the ten from dummy, partner's queen wins the trick with declarer playing the three. Partner returns the six of hearts and declarer plays the eight. Which heart do you play and why?
Partner has KQxx(x) of hearts, when you get in with the diamond jack (or spade ace) you will play the heart jack. Unless you have played the nine of hearts on the second trick, if partner has five hearts, then he is on a guess as to whether you have lead from J54, in which case he must overtake to run the suit or from J954 in which case he must play low to avoid blocking the suit. If you unblock the heart nine then he can safely overtake in either case. Fortunately at the table three hearts a spade and a diamond were enough to beat the contract, but it could have gone more off.