Sharp reply regarding wrong (6)
I believe the answer is:
retort
'sharp reply' is the definition.
(I've seen this before)
'regarding wrong' is the wordplay.
'regarding' becomes 're'.
'wrong' becomes 'tort' (legal term).
're'+'tort'='RETORT'
(Other definitions for retort that I've seen before include "Snappy reply" , "Chem. flask; sharp answer" , "Respond" , "Answer back" , "Quick answer - laboratory vessel" .)