Hired killer disguised in hat has snared victim in the end (6)
I believe the answer is:
hitman
'hired killer' is the definition.
(I know this)
'disguised in hat has snared victim in the end' is the wordplay.
'disguised' indicates anagramming the letters.
'has snared' is an insertion indicator (inserted letters are trapped or snared).
'in the end' indicates one should take the final letters.
The last letter of 'victim' is 'm'.
'in'+'hat'='inhat'
'inhat' is an anagram of 'hitan'.
'hitan' enclosing 'm' is 'HITMAN'.
(Other definitions for hitman that I've seen before include "killer" , "offer?" , "Assassin" , "Hired gun" .)