Harmed old barrier first (7)
I believe the answer is:
damaged
'harmed' is the definition.
(I've seen this before)
'old barrier first' is the wordplay.
'old' becomes 'aged' (similar in meaning).
'barrier' becomes 'dam' (dam is a kind of barrier).
'first' is a charade indicator (letters next to each other).
'aged' put after 'dam' is 'DAMAGED'.
(Other definitions for damaged that I've seen before include "Marred" , "Harmed, injured or spoiled" , "in poor condition" , "Hurt" , "Impaired" .)