Cunning insult on the radio (7)
I believe the answer is:
sleight
'cunning' is the definition.
(I've seen this before)
'insult on the radio' is the wordplay.
'insult' becomes ''slight' (I've seen this in another clue).
'on the radio' indicates a 'sounds like' (homophone) clue.
'slight' is a homophone of 'SLEIGHT'.
(Other definitions for sleight that I've seen before include "Skilful deception" , "Handy skill" , "distraction?" , "Trickery" , "Tricky cunning" .)