Source: Bridge Conventions in Depth By Matthew Granovetter, Pamela Granovetter
World Champion Eric Rodwell has made a number of contributions to bidding theory, but perhaps the most widely adopted of them is the Support Double. The Support Double, in case you”re not familiar with it, works like this:
Now West has these options:
2
fourcard spade
support dbl three-card spade support
pass fewer than three spades
This is very handy because when East holds only a four-card spade suit, he knows if he”s on a seven-card fit as opposed to an eight-card fit and he can decide whether to compete further in his suit. However, the price you pay is losing the penalty double. It has become popular to “slip in” lead-directing bids, because players know they can”t get penalized, but it”s a shame to let them bid defensively with no risk. Even when an opponent has a good hand for his “sandwich” overcall (an overcall between two bidders), there are chances for juicy penalties… if you can double. For example:
Using Support Doubles, West must pass, and East will rebid 2. Without Support Doubles, West doubles two clubs and collects 500 or 800. Another advantage of raising with three trumps rather than making a Support Double is that your raise takes up their valuable bidding space. For example:
Compare the support double auction:
Resulting in N/S 620, with the natural raise auction:
Resulting in N/S 110.
Finally and ironically, sometimes the support double takes up your own bidding space:
East-West result: 100. Whose fault is this one, East”s or West”s? We casino online don”t know, but their auction was certainly problematic. Here they are, on a finesse for 6
, settling for 100 defending 3. Without the Support Double, the auction goes:
and East-West score 600.
The Support Double showed:
– three hearts
– a hand of any strength
The natural two-club bid showed:
— five diamonds
– four or more clubs
– a good hand (for the vulnerable free bid)
Clearly, much more information was conveyed with the natural bid. One last thing to consider on the Support Double side — suppose West had five hearts and three diamonds: 
Notice that nothing has been lost. West still has enough to bid four diamonds freely, and this time he”ll pass East”s four-heart bid. If South bids four spades instead of three, it”s true that East-West will lose their eight-card heart fit (West will bid 5 ), but that”s a loss of only 50 points ( 600 instead of 650).