Start working with television (5)
I believe the answer is:
onset
'start' is the definition.
(onset is a kind of start)
'working with television' is the wordplay.
'working' becomes 'on'.
'with' is a charade indicator (letters next to each other).
'television' becomes 'set' (I've seen this in other clues).
'on'+'set'='ONSET'
(Other definitions for onset that I've seen before include "Assault; beginning" , "17 down [ASSAULT]" , "Kick-off" , "Advent" , "Assault; start" .)