Thwart with crushed filo (4)
I believe the answer is:
foil
'thwart' is the definition.
(I know that thwart can be written as foil)
'crushed filo' is the wordplay.
'crushed' indicates anagramming the letters.
'filo' anagrammed gives 'FOIL'.
'with' acts as a link.
(Other definitions for foil that I've seen before include "Hinder - prevent" , "Thin metal sheet; frustrate" , "Frustrate - sheet - rapier" , "hamper" , "Frustrate; kitchen wrap" .)