Knocking about with sailor on drugs (7)
I believe the answer is:
abusing
'knocking about' is the definition.
(knock about can mean to abuse)
'with sailor on drugs' is the wordplay.
'with' means one lot of letters go next to another.
'sailor' becomes 'ab' (abbreviation for able seaman).
'on drugs' becomes 'using' (I've seen this in another clue).
'ab'+'using' is 'ABUSING'.
(Other definitions for abusing that I've seen before include "Swearing" , "Treating badly" , "Taking undue advantage of and reviling" .)