When damaged, cut down (4)
I believe the answer is:
hewn
'cut down' is the definition.
('hewn' can be a synonym of 'cut down')
'when damaged' is the wordplay.
'damaged' indicates anagramming the letters.
'when' is an anagram of 'HEWN'.
(Other definitions for hewn that I've seen before include "Cut with an axe or chisel" , "Axed" , "Cut - carved - chopped" , "Hacked" , "Sculpted" .)