Backdrop is going down (7)
I believe the answer is:
setting
This clue is a double definition.
'backdrop' is the first definition.
(I've seen this in another clue)
'is going down' is the second definition.
(I've seen this in another clue)
(Other definitions for setting that I've seen before include "approaching the horizon" , "styling hair" , "An event's location; hardening" , "Environment" , "situation" .)