Traitor shot, on film (8)
I believe the answer is:
turncoat
'traitor' is the definition.
(I know that turncoat is a type of traitor)
'shot on film' is the wordplay.
'shot' becomes 'turn' (both can mean someone's attempt or go at something).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'film' becomes 'coat' (I've seen this in other clues).
'turn'+'coat'='TURNCOAT'
(Other definitions for turncoat that I've seen before include "Deserter to opposition" , "Traitor with reversed garment" , "treacherous as one?" , "Judas" , "Traitor, defector" .)