Green comes after a stop (5)
I believe the answer is:
avert
'stop' is the definition.
(to avert something is to stop or prevent it)
'green comes after a' is the wordplay.
'green' becomes 'vert' (heraldic term for green).
'comes after' is a charade indicator (letters next to each other).
'vert' put after 'a' is 'AVERT'.
(Other definitions for avert that I've seen before include "Turn aside, prevent" , "Prevent from occurring" , "Turn aside or ward off" , "Fend off" , "Head off" .)