This is aHand:

East (your right-hand opponent) reaches 4♠ after you have entered the auction with 2♥. You lead the ♥A and contemplate a shapely dummy. How should you defend?

Well, you must cash two rounds of Hearts to start with, to see how the land lies. When partner follows upwards he must have started with three cards in the suit (with only two he would have played high-low to tell you to continue with Hearts). So what do you do at trick three?

You might continue with Hearts, forcing declarer to ruff (in many cases, that’s your best defense as it weakens declarer’s trump holding). You might switch to a trump. Playing a Club or a Diamond seems to be pointless. Why?

Well, there’s rarely any good reason to lead dummy’s side-suit. Any tricks you may have there can hardly run away (how could declarer throw any losing Clubs away?) There’s also little point in leading a Diamond – all you will do is clear the path for Diamond ruffs on table.

Your best defense is to switch to a Spade, removing one of dummy’s trumps. If declarer is unable to run of the Club suit then his only alternative play – ruffing Diamond losers on table – will be compromised.

As it happens, this attack is a body blow to declarer. He wins on table and leads a Diamond but partner steps up with his ♦A and applies the knock-out blow by leading a second round of trumps. The first Spade leaves declarer groggy – the second round leaves him flat on the canvas. Unable to ruff all of his losers on table East has to concede defeat.

Yes, this is Hand 1 again, rotated 90°, with a small modification.