This hand serves as almost a perfect illustration for a lesson in takeout doubles and for converting a takeout double to a penalty double. East has a hand that qualifies as a light opening bid, the 11 high card points bolstered by a six card suit. South has a classic takeout double, saying "Partner, I have at least 3 card support in the unbid suits and the equivalent of an opening hand." So far, the auction is normal. When north passes the double, he indicates that he controls the spade suit and is willing to defend at the level of 1 spade. We can see that he has a solid holding in the spade suit, since he will lose only to the ace and king, and will be able to draw declarer's trumps. The ace of diamonds is a bonus, making the pass of the double even more compelling.
The auction shown below took place at the table, and departs from the expected when opener rebid his spades, explaining to his partner after the hand that he was trying to talk the defenders out of the double. South's second double shows that the hand is more that a minimum and north was even happier to convert to penalties.
The upshot of the hand was that declarer took precisely 3 tricks, the ace-king of trumps and one more trump when he trumped the third club lead by south. After that, the defenders were able to draw all his trumps and take the rest of the tricks in diamonds and clubs, as well as the ace of hearts. Down 5 doubled not vulnerable is 1,100 points, a very good score for north-south compared to the 600 that they could make in 3 notrump vulnerable. Another lesson to be taken would be, when you find yourself in a hole, stop digging!