Return catches weapon (4)
I believe the answer is:
sten
'weapon' is the definition.
(I've seen this before)
'return catches' is the wordplay.
'return' shows that the letters should be reversed in order.
'catches' becomes 'nets' (netting is a kind of catching).
'nets' reversed gives 'STEN'.
(Other definitions for sten that I've seen before include "dart of pain to Rob Roy, say" , "Type of light WWII machine gun" , "weaponry" , "British WWII submachine gun" , "Light portable submachine-gun" .)