Attack on filming location (5)

I believe the answer is:

onset

'attack' is the definition.
(archaic term for a military attack)

'on filming location' is the wordplay.
'filming location' becomes 'set' (I've seen this in another clue).
'on'+'set'='ONSET'

(Other definitions for onset that I've seen before include "Beginning or early stages" , "origin" , "Initial stage; attack" , "starting?" , "Start - opening moments" .)

I've seen this clue in The Guardian.

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