Stand up to female champion (4)
I believe the answer is:
face
'stand up to' is the definition.
(thesaurus)
'female champion' is the wordplay.
'female' becomes 'f' (common abbreviation).
'champion' becomes 'ace' (both can mean a person excelling at something).
'f'+'ace'='FACE'
(Other definitions for face that I've seen before include "set of features" , "Outward appearance" , "Cope with" , "steep side of mountain" , "Countenance, visage" .)