Ensnaring line, annoy fisherman (6)
I believe the answer is:
angler
'fisherman' is the definition.
(angler is a kind of fisherman)
'ensnaring line annoy' is the wordplay.
'ensnaring' means one lot of letters goes inside another (I've seen this in other clues).
'line' becomes 'l'.
'annoy' becomes 'anger' (I've seen this before).
'l' put within 'anger' is 'ANGLER'.
(Other definitions for angler that I've seen before include "I cast Rod" , "He fishes with rod and line" , "Isaac Walton wrote of the 'Compleat' one" , "Hook and line fisherman" , "person hoping to catch fish" .)