Competitor cheated badly, receives sanction (10)
I believe the answer is:
decathlete
'competitor' is the definition.
(I have seen 'versatile competitor' mean 'decathlete' so perhaps 'competitor' could also mean 'decathlete')
'cheated badly receives sanction' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'receives' is an insertion indicator (inserted letters are received).
'sanction' becomes 'let' (sanction can mean to allow or permit).
'cheated' with letters rearranged gives 'decathe'.
'decathe' enclosing 'let' is 'DECATHLETE'.
(Other definitions for decathlete that I've seen before include "All-rounder" , "versatile competitor" , "sportsman" .)