Other ranks caught a killer whale (4)
I believe the answer is:
orca
'killer whale' is the definition.
('orca' can be a synonym of 'killer whale')
'other ranks caught a' is the wordplay.
'other ranks' becomes 'or' (military abbreviation).
'caught' becomes 'c' (cricket abbreviation).
'or'+'c'+'a'='ORCA'
(Other definitions for orca that I've seen before include "Massive killer" , "Sea creature" , "Killer at sea" , "Marine creature" , "Large mammal" .)