Crab? Silly oaf does (7)
I believe the answer is:
seafood
'crab?' is the definition.
(crab is a kind of seafood)
'silly oaf does' is the wordplay.
'silly' indicates anagramming the letters.
'oaf'+'does'='oafdoes'
'oafdoes' with letters rearranged gives 'SEAFOOD'.
(Other definitions for seafood that I've seen before include "Eaten fish and shellfish" , "Edible fish, shellfish etc from the oceans" , "The "surf" of a surf 'n' turf dish" , "Shellfish, marine fish" , "Such as prawns, tuna" .)