The support double is a term used in the card game contract bridge. It is made by the opener after his right-hand opponent overcalls his partner's response to his opening bid,
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The Support double is a bridge convention invented by Eric Rodwell as a way of clarifying the amount of support held for your partner. It is normally used by the opening bidder in a competitive auction. The support double shows three-card support, no more and no less.
The convention came as result of the problem that, in competitive auctions, the opening bidder would often like to show 3-card support for partner's suit. However distinguishing between 4-card and 3-card support is important. 4-3 fits ("Moysian fits") don't play as well as real, 8+-card fits. Those situations occur much more frequently than the hands where the opening bidder would like to bid a penalty double over a 1-level overcall, thus the idea of replacing that "standard" usage with the conventional one.
The Support Double is generally applied whenever partner of the opening bidder names a new suit and there has been interference by an opponent. In other words, the Support Double normally applies after an opening on the one level has been followed by a suggestion by partner of a new suit and an overcall or raise by the fourth player.
The Support Double can also be applied when both opponents bid. The key is that the support doubler has opened , partner has replied in a new suit and the next player has made a bid.
The difference between a one-level raise or jump raise in the new suit, named by the responder and a Support Double by the opening bidder is the amount of cards for the suit support. A direct raise shows four+ card support, a support double shows exactly three card support.
Take the following auction:
| West | North | East | South |
|---|---|---|---|
| pass | 1♣ | pass | 1♥ |
| 1♠ | double | pass | 1NT |
| pass |
Playing support doubles, North, the opener, has shown three-card support for South's 1♥ call. This is important because South might only have four hearts. Based on the South no trump bid, it can be assumed that South doesn't have 5 or more hearts.
Hand in hand with the support double is the Support redouble which also shows three card support. Examine this auction, which is similar to the one above.
| West | North | East | South |
|---|---|---|---|
| pass | 1♣ | pass | 1♥ |
| double | redouble |
North has shown three-card support for South's heart suit. South uses this information to form the next bid.
Support doubles are not used (except by special agreement) by partner of an overcaller.
| West | North | East | South |
|---|---|---|---|
| 1♦ | 1♠ | 2♣ | Double |
The assumption is that the overcaller must surely have at least 5 cards in the suit he has bid. As such a simple raise is normally sufficient to show some points and support. In such a situation, a double by the partner of the overcaller would be treated as either a Rosenkranz double, a responsive double or a penalty double based on partnership agreement.
The above examples show the support double's use over 1 level overcalls. Partnerships usually decide to play support doubles through 2 Hearts or 2 Spades. Here are several other less discussed examples but nonetheless valid examples of normal support doubles
| West | North | East | South |
|---|---|---|---|
| pass | 1♣ | 1 ♥ | 1♠ |
| 2 ♥ | double |
Playing negative doubles or NOT, opener's double shows three spades. It is irrelevant that opener knows that partner has 5 spades (if playing negative doubles), the double shows three card support. The principle is that you and your partner use the opponent's bidding to assist your bidding. Clarify right now if you have 3 or four card support unless you have something else very important to say.
| West | North | East | South |
|---|---|---|---|
| 1♦ | 1 ♥ | 2♣ | 2 ♦ |
| double |
In this case with a really competitive auction, someone is probably stretching their bid.
West has opened and his partner has shown 5 clubs and 10 points yet South is showing a limit raise of Hearts.
The double is still support. It is particularly important in this instance. BTW:The most likely culprit is South.
There is a lot of literature for advancing players on the importance of determining 8 vs 9 card fits. Here is one example of its importance: As East, your hand is xxxxx, xx, void, KQxxxx The auction is
| West | North | East | South |
|---|---|---|---|
| 1♣ | 1 ♥ | 1 ♠ | 2 ♥ |
| 2 ♠ |
Without knowing RHO's next bid, if East knows there is a 9 card spade fit, East can bid 4 Spades even in an IMP game and expect a good chance to make it. However think about the same auction if partner doubles showing exactly 3 spades. This commentator thinks your bid now becomes a guess.
In American Contract Bridge League (ACBL) tournaments, support doubles must be indicated on the convention card and must be Alerted. Additionally, when opener makes a call other than a support double (including Pass) when the support double is an option, an Alert should be made if the partnership agreement is that opener's failure to double or to raise denies 3-card or longer support for responder's suit (normally, one would expect only 4-card or longer support to be denied by failure to raise responder's major suit). Per the "Alert Procedures" page on the ACBL website: "In general, when the use of conventions leads to unexpected understandings about suit length by negative inference, a natural call becomes Alertable." While the ACBL does make an exception for agreements that "have become expected and are fairly common," the fact that the ACBL continues to require an Alert for the support double itself argues against applying this exception; the requirement to Alert implies that the support double is not considered "expected... and fairly common" to date.[1]
Most bridge clubs require a partnership to employ active ethics, and the partnership should disclose all relevant agreements to the opponents. Secret conventions are not allowed.