When your opponent opens with a Precision (or any other Strong, Forcing and Artificial) 1, I recommend trying to interfere. Best is to preempt (the higher the better), but if you can't preempt, it is useful to be able to show a 2-suiter and hope partner can preempt.
CRASH is a method to show all 2-suiters. I won't specify the length/strength requirements. Let vulnerability be the guide. The more vulnerable you are, the better the suit quality and length. At least 5-4 is normal, but at Favorable, I suppose 4-4 is possible. Here are what the bids mean after their Precision 1 opening:
Double=Color: Two suits of the same color-- reds or blacks (+ or +)
1=Rank: Two suits of the same rank -- majors or minors (+ or +)
1NT=Shape -- Two suits of the same shape -- round or pointed (+ or +)
Other bids (jumps or not) = Natural (one suited).
The mnemonic memory device uses the letters in the word CRASH to stand for: Color, RAnk, SHape. They are in order of the 3 artificial calls (Double, 1 and 1NT).
After the auction begins 1 Pass 1 (where 1 is the artificial negative response), CRASH is still on. This time, though, there is no 1 overcall available, so the 3 CRASH bids in order are : Double, 1NT and 2 to show Color, RAnk and SHape. All other calls are natural. If they respond anything other than 1, the CRASH system is off.
Note: This is only for very experienced players. Aside from remembering the initial bids, it is important to discuss follow-ups. For example, what does the partner of the CRASHer do? All of his bids on any level should be "Pass/Correct." He should bid to the highest level he can comfortably preempt to. Example:
3 means that South is willing to play on the 3-level in diamonds if that is one of the CRASHER's suits. If the CRASHER does not have diamonds, he has to correct to his cheapest suit (in this case, since he showed majors or minors, and he lacks diamonds, he must have +, so he corrects to 3). This requires lots of experience! Also, you need to know what happens if they double the initial CRASH bid. Furthermore, what if the partner of the CRASHER has his own 1-suiter and doesn't want to make a Pass/Correct bid? In that case, he is supposed to bid NOTRUMP, requesting a relay to CLUBS -- so he can show his own 1-suiter. If you are still reading, then maybe this convention is for you.
CRASH can also be used after the opponents open 2.
All bids in this system (by the CRASHer and his partner) are alertable.
last updated: June 2012