Wrong pace when retreating (4)
I believe the answer is:
tort
'wrong' is the definition.
(legal term)
'pace when retreating' is the wordplay.
'pace' becomes 'trot' (I've seen this in another clue).
'when retreating' shows that the letters should be reversed in order.
'trot' reversed gives 'TORT'.
(Other definitions for tort that I've seen before include "Legal wrong for which damages may be sought" , "Wrongful act (in law)" , "Trot to get legal wrong" , "Wrongdoing for which damages may be sought" , "Private or civil wrong open to damages" .)