Upended in grass, outhouse damaged (9)
I believe the answer is:
tarnished
'damaged' is the definition.
('tarnished' can be a synonym of 'damaged')
'upended in grass outhouse' is the wordplay.
'upended' shows that the letters should be reversed in order (in a down clue, letters go up).
'grass' becomes 'rat' (I've seen this before**).
'outhouse' becomes 'shed' (I've seen this before).
'in'+'rat'='inrat'
'inrat' back-to-front is 'tarni'.
'tarni'+'shed'='TARNISHED'
(Other definitions for tarnished that I've seen before include "Sullied" , "Blemished" , "Stained" , "Dulled, discoloured" , "Having lost lustre" .)