Fellow with line in excellent restraint (7)
I believe the answer is:
manacle
'restraint' is the definition.
(manacle is a kind of restraint)
'fellow with line in excellent' is the wordplay.
'fellow with' becomes 'man' (I've seen this in other clues).
'line' becomes 'l'.
'in' is an insertion indicator.
'excellent' becomes 'ace' (I've seen this before).
'l' inserted into 'ace' is 'acle'.
'man'+'acle'='MANACLE'
(Other definitions for manacle that I've seen before include "Fetter" , "Curb" , "restricting at the cuff?" , "Shackle on the wrist" , "Handcuff" .)