Guy in distress is a knight (7)
I believe the answer is:
paladin
'knight' is the definition.
(I've seen this before)
'guy in distress' is the wordplay.
'guy' becomes 'lad' (both can mean a man or boy).
'in' means one lot of letters goes inside another.
'distress' becomes 'pain' (I've seen this before).
'lad' going into 'pain' is 'PALADIN'.
'is a' acts as a link.
(Other definitions for paladin that I've seen before include "hero" , "Knightly champion" , "Historical knight" , "Knight errant; a peer of Charlemagne" , "Chivalrous knight" .)