Smashed copper treadle's repaired (9)
I believe the answer is:
plastered
'smashed' is the definition.
(I know that smashed can be written as plastered)
'copper treadle's repaired' is the wordplay.
'copper' becomes 'p'.
'repaired' indicates anagramming the letters.
'treadles' anagrammed gives 'lastered'.
'p'+'lastered'='PLASTERED'
(Other definitions for plastered that I've seen before include "the worse for drink" , "like walls and ceilings?" , "Like member in cast" , "Pickled" , "Drunk (slang)" .)