Nails badly finished off (5)
I believe the answer is:
slain
'finished off' is the definition.
(I've seen this in another clue)
'nails badly' is the wordplay.
'badly' indicates anagramming the letters (letters in the wrong order).
'nails' anagrammed gives 'SLAIN'.
(Other definitions for slain that I've seen before include "Put to the sword" , "Killed, murdered" , "Slaughtered" , "Violently killed" .)