Back complaint (7)
I believe the answer is:
lumbago
'back complaint' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for lumbago that I've seen before include "Gaul mob (anag.)" , "Back affliction" , "Pain -- a bum log (anag)" , "Rheumatic pain in muscles of lower back" , "Maul bog badly for a rheumatic affliction" .)