Agent's player after flying start (6)
I believe the answer is:
factor
'agent's' is the definition.
(business term for a representative)
'player after flying start' is the wordplay.
'player' becomes 'actor' ('actor' can be a synonym of 'player'**).
'after' is a charade indicator (letters next to each other).
'start' suggests taking the first letters.
The initial letter of 'flying' is 'f'.
'actor' put after 'f' is 'FACTOR'.
(Other definitions for factor that I've seen before include "Cause" , "one to be taken into account" , "Reason" , "Mathematical quantity" , "Circumstance that contributes toward a result - arithmetically?" .)