A policeman and a man that is out to obstruct (6)
I believe the answer is:
impede
'obstruct' is the definition.
('impede' can be a synonym of 'obstruct')
'a policeman and a man that is out' is the wordplay.
'a policeman' becomes 'mp' (abbreviation for Military Policeman).
'and' is a charade indicator (letters next to each other).
'a man' becomes 'ed' (**).
'that is' becomes 'ie' ('i.e.' can be a synonym of 'that is').
'out' is an insertion indicator.
'mp'+'ed'='mped'
'mped' inserted inside 'ie' is 'IMPEDE'.
'to' is the link.
(Other definitions for impede that I've seen before include "Obstruct, hold up progress" , "Delay or obstruct" , "Cramp" , "Put obstacle in the way, hinder" , "Handicap" .)