Fish cut up with great force (8)
I believe the answer is:
pilchard
'fish' is the definition.
(pilchard is a kind of fish)
'cut up with great force' is the wordplay.
'cut' becomes 'clip' (clip is a kind of cut**).
'up' shows that the letters should be reversed in order (in down clue: letters go upwards).
'with great force' becomes 'hard' ('hard' can be a synonym of 'with great force').
'clip' backwards is 'pilc'.
'pilc'+'hard'='PILCHARD'
(Other definitions for pilchard that I've seen before include "Small marine food fish" , "Small fatty fish, usually tinned" , "Edible herring relative" , "'Small fatty fish, usually canned (8)'" , "Fish of herring family" .)