Hardened to being badly ruined (6)
I believe the answer is:
inured
'hardened to' is the definition.
(I've seen this in another clue)
'badly ruined' is the wordplay.
'badly' indicates an anagram (letters in the wrong order).
'ruined' is an anagram of 'INURED'.
'being' acts as a link.
(Other definitions for inured that I've seen before include "Hardened against, toughened" , "Hardened, accustomed" , "Hardened, perhaps ruined" , "Accustomed to something difficult" , "Habituated or hardened" .)