Run, champion, run! (4)
I believe the answer is:
race
'run' is the definition.
(synonyms)
'run champion' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'champion' becomes 'ace' (both can mean a person excelling at something).
'r'+'ace'='RACE'
(Other definitions for race that I've seen before include "Run swiftly" , "Career - people" , "Rush" , "People; run" , "Running contest" .)