Hurt boxing schoolboy champion (7)
I believe the answer is:
paladin
'champion' is the definition.
(I know that champion can be written as paladin)
'hurt boxing schoolboy' is the wordplay.
'hurt' becomes 'pain' (synonyms).
'boxing' means one lot of letters goes inside another ('box' can mean contain, as in to put in a box).
'schoolboy' becomes 'lad' (lad can mean a young boy).
'pain' placed around 'lad' is 'PALADIN'.
(Other definitions for paladin that I've seen before include "One of the twelve peers at Charlemagne's court - heroic champion" , "Knightly champion" , "Chivalrous knight" , "Historical knight" , "Knight errant; a peer of Charlemagne" .)