Has to admit an officer to make arrests (5)
I believe the answer is:
halts
'arrests' is the definition.
('halt' can be a synonym of 'arrest')
'has to admit an officer' is the wordplay.
'to admit' indicates putting letters inside.
'an officer' becomes 'lt' (abbreviation for lieutenant).
'has' going around 'lt' is 'HALTS'.
'to make' is the link.
(Other definitions for halts that I've seen before include "Brings to an end" , "Stops moving or progress" .)