Defeat; strike (4)
I believe the answer is:
beat
I believe this clue is a double definition.
'defeat' is the first definition.
(I know that beat is a more specific form of defeat)
'strike' is the second definition.
(I know that beat is a more specific form of strike)
(Other definitions for beat that I've seen before include "Master" , "Get the better of in competition" , "Policeman's regular route" , "course for law enforcement officers" , "Baffle - all in" .)