Is he right to do wrong? (3)
I believe the answer is:
rod
'is he' is the definition.
'right to do wrong?' is the wordplay.
'right' becomes 'r' (common abbreviation).
'wrong?' is an anagram indicator (I've seen 'wrong' mean this).
'do' is an anagram of 'od'.
'r'+'od'='ROD'
(Other definitions for rod that I've seen before include "Little boy" , "See 13" , "Long, straight stick" , "16.5 feet" , "A few yards" .)