Footage upset tough little swimmer (8)
I believe the answer is:
pilchard
'little swimmer' is the definition.
(pilchards are small fish)
'footage upset tough' is the wordplay.
'footage' becomes 'clip' (film clip).
'upset' says the letters should be written backwards.
'tough' becomes 'hard' (synonyms).
'clip' reversed gives 'pilc'.
'pilc'+'hard'='PILCHARD'
(Other definitions for pilchard that I've seen before include "Edible herring relative" , "Small marine food fish" , "'Small fatty fish, usually canned (8)'" , "Small fatty fish, usually tinned" , "Small sea fish related to the herring" .)