Fisherman's rage holding line (6)
I believe the answer is:
angler
'fisherman's' is the definition.
(angler is a kind of fisherman)
'rage holding line' is the wordplay.
'rage' becomes 'anger' (I've seen this in other clues).
'holding' means one lot of letters goes inside another.
'line' becomes 'l' (used when specifying particular lines from a poem).
'anger' going around 'l' is 'ANGLER'.
(Other definitions for angler that I've seen before include "Sportsman" , "Fisher with rod and line" , "I cast Rod" , "who looks for compliments" , "Fisher with hook and line." .)