Harm barrier with endless rages (6)
'harm' is the definition.
('damage' can be a synonym of 'harm')
'barrier with endless rages' is the wordplay.
'barrier' becomes 'dam' (dam is a kind of barrier).
'with' means one lot of letters go next to another.
'endless' indicates the central letters.
The central letters of 'rages' are 'age'.
(Other definitions for damage that I've seen before include "Harm, injury", "Impairment, injury", "vandalism?", "'Deface, impair (6)'", "Cost (slang)".)