Material if crab is used (6)
I believe the answer is:
fabric
'material' is the definition.
(I know that material can be written as fabric)
'if crab is used' is the wordplay.
'is used' indicates an anagram.
'if'+'crab'='ifcrab'
'ifcrab' with letters rearranged gives 'FABRIC'.
(Other definitions for fabric that I've seen before include "stuff" , "Knitted or woven fabric" , "(Texture of) cloth" , "Cloth, woven material" , "Perhaps felt" .)