Rag supports broadcast (5)
I believe the answer is:
tease
'rag' is the definition.
(I've seen this before)
'supports broadcast' is the wordplay.
'supports' becomes 'tees' (tee is a kind of support).
'broadcast' indicates a 'sounds like' (homophone) clue (how the word might sound on the radio or TV).
'tees' sounds like 'TEASE'.
(Other definitions for tease that I've seen before include "Vex" , "Rib, wind up" , "Comb or card (wool)" , "Make fun of; comb wool" , "Gently mock" .)