Mean to back up the law and roll in the mud (6)
I believe the answer is:
wallow
'roll in the mud' is the definition.
(I've seen this before)
'mean to back up the law' is the wordplay.
'mean' becomes 'low' (both can mean nasty or dishonourable).
'to' means one lot of letters go next to another (I've seen this in other clues).
'back up' says the letters should be written backwards (I've seen 'backed up' mean this).
'law' in reverse letter order is 'wal'.
'low' after 'wal' is 'WALLOW'.
'and' acts as a link.
(Other definitions for wallow that I've seen before include "Lie about in mud or water" , "Luxuriate (in mud, muck)" , "Indulge excessively, in self-pity perhaps" , "Roll about as in water or mud" , "Roll around as in mud" .)