Broadcast topless contest (4)
I believe the answer is:
vent
'broadcast' is the definition.
(thesaurus)
'topless contest' is the wordplay.
'topless' means to remove the first letter.
'contest' becomes 'event' (I've seen this before).
'event' with its first letter removed is 'VENT'.
(Other definitions for vent that I've seen before include "Small outlet" , "Opening releasing gas" , "Broadcast" , "Slit in the back of a jacket" , "[BLOWHOLE] ?" .)