Redcap in old film freed from obligation (6)
I believe the answer is:
exempt
'freed from obligation' is the definition.
(I've seen this before)
'redcap in old film' is the wordplay.
'redcap' becomes 'mp'.
'in' is an insertion indicator.
'old' becomes 'ex'.
'film' becomes 'et'.
'ex'+'et'='exet'
'mp' inserted into 'exet' is 'EXEMPT'.
(Other definitions for exempt that I've seen before include "Free (from obligation)" , "Excused - let off" , "not expected to pay" , "Free (from taxes, etc)" , "Not subject to a law" .)