Chivalrous champion of a person in pain (7)
I believe the answer is:
paladin
'chivalrous champion' is the definition.
'a person in pain' is the wordplay.
'a person' becomes 'lad' (lad is a kind of person).
'in' means one lot of letters goes inside another.
'lad' put within 'pain' is 'PALADIN'.
'of' is the link.
(Other definitions for paladin that I've seen before include "Medieval champion" , "Historical knight" , "Knight errant; a peer of Charlemagne" , "hero" , "One of the twelve peers at Charlemagne's court - heroic champion" .)