Policeman injecting horse will get the axe (7)
I believe the answer is:
chopper
'the axe' is the definition.
(I've seen this before)
'policeman injecting horse' is the wordplay.
'policeman' becomes 'copper' (copper can informally mean a police officer).
'injecting' indicates putting letters inside.
'horse' becomes 'H' (abbreviation as in horse power).
'copper' going around 'h' is 'CHOPPER'.
'will get' is the link.
(Other definitions for chopper that I've seen before include "that's used by a lumberjack" , "type of aircraft" , "Air transport" , "Blade" , "Small axe" .)