The origin of this conventional defense mechanism is unknown. It is employed after an opponent has opened the auction with a strong, artificial 1 Club, which has variable meanings. As a defense mechanism DOBC was devised to interfere and possibly find an immediate fit even on the one level as quickly as possible, and then cease competition.
The following overcalls by the intervenor are as follows:
Intervenor Meaning Double: Promises a one-suited holding and possibly strong values. 1 : Promises Diamonds and a second, unspecified second suit. 1 : Promises Hearts plus Spades or Clubs. The second suit can be shown in later bidding. 1 : Promises Spades and Clubs. 1NT: Shows a shortage in Clubs. 2 : Shows a singleton or void in Clubs.
The distribution of the one-suited holding should be at least a solid 5-card suit to a semi-solid 6-card suit. The distribution of the two-suited holdings should be at least 4-4 with honors located in the two intended suits. Otherwise the distribution should be at least a 5-4 minimum by favorable vulnerability and at least a 5-5 by non-favorable vulnerability.
These bids represent only the overcalls of the intervenor. All continuances are a matter of partnership agreement.
If you wish to include this feature, or any other feature, of the game of bridge in your partnership agreement, then please make certain that the concept is understood by both partners. Be aware whether or not the feature is alertable or not and whether an announcement should or must be made. Check with the governing body and/or the bridge district and/or the bridge unit prior to the game to establish the guidelines applied. Please include the particular feature on your convention card in order that your opponents are also aware of this feature during the bidding process, since this information must be made known to them according to the Laws of Duplicate Contract Bridge. We do not always include the procedure regarding Alerts and/or Announcements, since these regulations are changed and revised during time by the governing body. It is our intention only to present the information as concisely and as accurately as possible.
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