Fish cutting back, powerfully (8)
I believe the answer is:
pilchard
'fish' is the definition.
(pilchard is a kind of fish)
'cutting back powerfully' is the wordplay.
'cutting' becomes 'clip' (clip is a kind of cutting).
'back' shows that the letters should be reversed in order.
'powerfully' becomes 'hard' (eg in 'ran hard').
'clip' written backwards gives 'pilc'.
'pilc'+'hard'='PILCHARD'
(Other definitions for pilchard that I've seen before include "Small sea fish related to the herring" , "Item of seafood" , "type of fish" , "Small marine food fish" , "Edible herring relative" .)