Assault at filming location (5)
I believe the answer is:
onset
'assault' is the definition.
(I've seen this before)
'at filming location' is the wordplay.
'at' becomes 'on' (location).
'filming location' becomes 'set' (I've seen this in another clue).
'on'+'set'='ONSET'
(Other definitions for onset that I've seen before include "Advent" , "Inception" , "Cast stone in attack" , "Assault; beginning" , "Start - notes (anag)" .)