Opportunity backed after complaint -- game might be raised here (6,4)
I believe the answer is:
grouse moor
'game might be raised here' is the definition.
(grouse are game birds)
'opportunity backed after complaint' is the wordplay.
'opportunity' becomes 'room' (room or space to do something).
'backed' says the letters should be written in reverse.
'after' means one lot of letters go next to another.
'complaint' becomes 'grouse' (I've seen this before).
'room' in reverse letter order is 'moor'.
'moor' after 'grouse' is 'GROUSE MOOR'.
(Other definitions for grouse moor that I've seen before include "place for sport" , "reserve for game" , "Bird shooting land" .)