Agent set up one-time entertainer (9)
I believe the answer is:
performer
'entertainer' is the definition.
(performer is a kind of entertainer)
'agent set up one-time' is the wordplay.
'agent' becomes 'rep' (short for representative).
'set up' says the letters should be written in reverse.
'one-time' becomes 'former' (I've seen this before).
'rep' back-to-front is 'per'.
'per'+'former'='PERFORMER'
(Other definitions for performer that I've seen before include "Fred Astaire, say" , "player" , "star?" , "Thespian" , "Eg 9 [ACTRESS]" .)