Cast finished broadcast (5)
I believe the answer is:
threw
'cast' is the definition.
(cast can mean to throw)
'finished broadcast' is the wordplay.
'finished' becomes 'through' (similar in meaning).
'broadcast' indicates a 'sounds like' (homophone) clue (how the word might sound on the radio or TV).
'through' is a homophone of 'THREW'.
(Other definitions for threw that I've seen before include "Cast" , "Disconcerted" , "Chucked" , "'Hurled, flung (5)'" , "Confused" .)