The idea of a penalty double comes from the very earliest form of bridge, (rubber bridge), which was generally played for money. Double was invented as a bid to increase the penalty when the opponents bid too much. Penalty doubles are very opposite of take out doubles (but they look the same; "X"). You need to be sure the opponents will fail when you double because If they make their (doubled) contract, they will score a very big bonus! The actual figure depends on the vulnerability. But still double for penalties, and if they make their contract, so what! A penalty double may be removed by bidding over it.
Having penalty doubles prevents the opponents from frivolously bidding too much over your contract. Eg: Suppose you can make a vulnerable game contract of 4♥. This would be worth 620 points. If the oppponents were non vulnerable and the penalty double didn’t exist, they could go down ten tricks and only lose 500 points (10 x 50), so they would overbid for sure. The penalty double is a deterrent against overbidding.
It is particularly dangerous to double the opponents in a partscore unless you are certain you can defeat them. If they make their partscore, the trick score is doubled, and they may receive the game bonus as well, if the total is 100 or more points. (2♥ or 2♠ doubled & making 8 tricks, vulnerable, will score 670, as opposed to 110 not doubled, & 3♦ or 3♣ doubled, will score 670).
How do you tell if a double is for penalty or takeout?
If your partner has not yet bid in the auction, and you double, this is for takeout, because you're asking them what they've got. e.g. 1♥ p 3♥ Double = take out with spades. But if you've already heard what they hold, e.g. 1♥ (2♣) 3♥, a double is for penalty, saying you don't believe they can make 3♥. Most doubles these days, particularly at low levels, are meant for takeout, meaning "Partner please bid you longest suit".
What do you need to make a penalty double?
(a) Doubling 1NT
You’re showing a hand with at least the upper point range of their opening. (eg if their 1NT shows 15- 17, you'd be showing 17+ high card points.) Imagine you have the hand below, and hear the opponent on your right open with 1NT
It will be hard for declarer to succeed in 1NT, with your strong hand sitting over them. Also, you have a long suit (eg ♥KQJ109), and entries, and you’re on lead, so make a penalty double. Lead your suit, and let declarer have an early trick there (eg the Ace, if they hold it), and then you've promoted four more tricks there. Of course, they may “run” from your double, and bid a suit. With the hand above you would now bid hearts at whatever level you wanted to.
(b) Doubling at High Levels
North East South West
2♠ p 4♠ ?
Double. North has opened with a weak –two bid, and based on West’s high card strength, South’s jump to 4♠ is likely to be a preemptive raise, trying to make it difficult for East West to enter the auction. Since North South are at the game level, West's double is for penalty. West could have bid 4NT as a take out.
The higher the opponents bid, the more likely your double is meant for penalty. If you have four of the opponents’ trumps and good ones, don’t enter the auction yourself, rather, wait and hope they will bid too high, then say “double”. Partner will know that you had a chance to double earlier, and didn’t.
To make a good penalty double, you need
A strong trump holding in the opponents’ suit (eg QJ109, or AQJ10)
A misfit with partner (where partner has bid)
Test your knowledge
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