Attack on television (5)
I believe the answer is:
onset
'attack' is the definition.
('onset' can be a synonym of 'attack')
'on television' is the wordplay.
'television' becomes 'set' (I've seen this in other clues).
'on'+'set'='ONSET'
(Other definitions for onset that I've seen before include "Advent" , "Initial stage; attack" , "Beginning; violent attack" , "Storming" , "First signs" .)