Briefly expose rear in movie scene (9)
I believe the answer is:
flashback
'briefly expose rear in movie scene' is the definition.
I can't tell whether this defines the answer.
'expose rear in movie scene' is the wordplay.
'expose' becomes 'flash' (flashing is a kind of exposing).
'rear in movie scene' becomes 'back' (I can't explain this - if you can you should give a lot more credence to this answer).
'flash'+'back'='FLASHBACK'
Can you help me to learn more?
(Other definitions for flashback that I've seen before include "Past scene inserted into a film's chronology" , "Film scene from an earlier time" , "Scene depicting previous events" , "Unexpected but vivid recurrence of a past experience" , "(In film or novel) return to a previous event or period" .)