Answer about an offence (6)
I believe the answer is:
retort
'answer' is the definition.
(retorting is a kind of answering)
'about an offence' is the wordplay.
'about' becomes 're' (common abbreviation for 'with reference to').
'an offence' becomes 'tort' (legal term for a type of offence).
're'+'tort'='RETORT'
(Other definitions for retort that I've seen before include "Sharp riposte" , "Come back" , "Answer sharply" , "Answer in retaliation" , "Quick and clever or angry reply" .)