In the game of contract bridge, CRASH (an acronym for Color-RAnk-SHape) is a defense against a strong 1♣ or a 1NT opening that first appeared in 1976 in an article by Kit Woolsey in The Bridge World.
[1] Within the CRASH framework, intervening calls after the 1NT opening denote either (a) two-suited hands of the same color (black or red), the same rank (major or minor), or the same shape (pointed or rounded)[2] or (b) a natural one-suited hand (hearts or spades).
Over a 1NT opening, the following CRASH overcall structure applies: Following the two-suited overcalls, advancer will bid taking into account that out of the two possible two-suited hands of intervenor, the likely holding is in advancer's shortest suits.
For instance, following a CRASH double, an advancer holding ♠ 1075 ♥ Q9842 ♦ KJ6 ♣ K3 will start from the assumption that intervenor holds length in the black suits in which advancer's maximum length is three cards, rather than in the red suits in which his maximum length is five cards.
Other defenses similar to CRASH, with the bids in a different order, include KOSHER and SHAKER.