Scowl from unyielding champion (7)
I believe the answer is:
grimace
'scowl' is the definition.
(I've seen this in another clue)
'unyielding champion' is the wordplay.
'unyielding' becomes 'grim' (I've seen this in another clue).
'champion' becomes 'ace' (both can mean a person excelling at something).
'grim'+'ace'='GRIMACE'
'from' acts as a link.
(Other definitions for grimace that I've seen before include "Facial expression showing disgust, wry humour etc" , "Dour" , "look disgusted" , "displeasure" , "betray disgust" .)