Halfwit on air with smug broadcast (9)
I believe the answer is:
ignoramus
'halfwit' is the definition.
'on air with smug broadcast' is the wordplay.
'with' says to put letters next to each other.
'broadcast' is an anagram indicator (letters scattered or cast around).
'on'+'air'='onair'
'onair' after 'smug' is 'smugonair'.
'smugonair' with letters rearranged gives 'IGNORAMUS'.
(Other definitions for ignoramus that I've seen before include "One could be blissful it's said" , "Simpleton" , "Stupid person" , "Uneducated person" , "Ron is a mug (anag.)" .)