Bird with an outsize victim (6)
I believe the answer is:
osprey
'bird' is the definition.
(osprey is a kind of bird)
'with an outsize victim' is the wordplay.
'with' is a charade indicator (letters next to each other).
'an outsize' becomes 'os'.
'victim' becomes 'prey' (prey is a kind of victim).
'os' next to 'prey' is 'OSPREY'.
(Other definitions for osprey that I've seen before include "Fish eagle" , "Large bird that preys on fish in inland waters" , "Large bird that fishes inland waters" , "Fish-eating 15 ac" , "Bird of fine feather" .)