Feedback on beginning of play being broadcast (8)
I believe the answer is:
reaction
'feedback' is the definition.
(I've seen this before)
'on beginning of play being broadcast' is the wordplay.
'on' becomes 're' (regarding).
'beginning of play' becomes 'Act I' (first act of a play).
'being broadcast' becomes 'on' (ie on TV or the radio).
're'+'acti'+'on'='REACTION'
(Other definitions for reaction that I've seen before include "Answer" , "Force" , "In mechanics, every action has an equal and opposite one" , "Creation found in response to event" , "Feedback" .)