Six, in all, were hacked to pieces by the scoundrel (7)
I believe the answer is:
villain
'the scoundrel' is the definition.
('villain' can be a synonym of 'scoundrel')
'six in all were hacked to pieces' is the wordplay.
I cannot really see how this works, but
'six' could be 'vi' (Roman numerals) and 'vi' is present in the answer.
'in' is found in the answer.
an anagram of 'all' is 'lla' which is present in the answer.
No letters remain.
This may be the basis of the clue (or it may be nonsense).
'by' acts as a link.
Can you help me to learn more?
(Other definitions for villain that I've seen before include "Wrongdoer" , "Criminal; stage baddy" , "Bad guy" , "Criminal, rogue" , "One played badly" .)