Our group back film? (7)
I believe the answer is:
western
'film?' is the definition.
(I know that Western is a type of film)
'our group back' is the wordplay.
'our group' becomes 'we' (we or us).
'back' becomes 'stern' (stern means the back of a boat).
'we'+'stern'='WESTERN'
(Other definitions for western that I've seen before include "Type of film or music" , "Cowboy film of occidental origin" , "Old film genre, horse opera" , "Cowboys and Indians film" , "The Occident" .)