Same agent changed what player's called (5,4)
I believe the answer is:
'what player's called' is the definition.
(an actor might use a stage name)
'same agent changed' is the wordplay.
'changed' indicates anagramming the letters.
'sameagent' anagrammed gives 'STAGE-NAME'.
(Other definitions for stage name that I've seen before include "Player could go by this" , "Actor's pseudonym" , "Lady Gaga, say" , "fresh identity" .)