Player's agent blowing top (5)
I believe the answer is:
actor
'player's' is the definition.
(I've seen this before)
'agent blowing top' is the wordplay.
'agent' becomes 'factor' (business term for a representative).
'blowing top' means to remove the first letter.
'factor' with its first letter removed is 'ACTOR'.
(Other definitions for actor that I've seen before include "Theatrical player" , "Theatre player" , "eg Anthony Hopkins" , "For example, Colman" , "Stage player" .)