This was a hand that occurred on Bridge Base Online. When one overcalls a weak three, one needs good shape and at least 16 points. One should be short in the pre-empt suit in length and in strength. In the balancing seat, one can be an Ace weaker but will also have good shape.
However, an exception would be with a long suit of your own. One is not supposed to pre-empt a pre-empt, but the very strong Spade suit (headed by AKQ) and a void make a Three Spade overcall marginally acceptable.
The Bidding: East, with a pretty strong suit, deemed it was worth an extra card and opened Three Diamonds. South overcalls Three Spades and West chimes in with Four Hearts.
East, with Heart tolerance and a suit headed by the AKQ, bids Five Diamonds. West has at most one Spade loser and bids Six. With a Diamond void or stiff, he would have bid Five Hearts. North has almost no defense and takes a save or sacrifice at Six Spades. West has to resign himself to whatever positive a double gives.
The Play: West leads a Spade to cut down ruffing value that a sacrifice often relies on. When South loses a Diamond, East wins and plays another trump. Declarer will lose no Spades, no Hearts, two Diamonds and two Clubs for down three and -500. This is an excellent sacrifice, because the opponents do not even get what they would get for a vulnerable game (620) not to mention the vulnerable slam (1370).
Alternate play: If West does not lead a Spade, declarer will lose a Diamond and two Clubs for -300, just as long as he comes back to his hand using a spade after the first ruff. When he takes the second Diamond ruff, West will not be able to ruff higher than dummy because his trump singleton will be gone. South cannot draw two rounds of trump because he needs three ruffs. After the second and third ruffs, he uses Heart ruffs as transportation.
East will ruff the third Heart ahead of declarer with the Spade Jack hoping for an uppercut. If partner had Q10 doubleton in trump, the Queen becomes promoted to a winner because the Jack will force declarer’s King. Unfortunately for the defense, West did not have the trump Queen.