Refuse to obey (4)
I believe the answer is:
defy
'refuse to obey' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for defy that I've seen before include "Openly resist (authority etc)" , "Refuse to obey (person)" , "Flout" , "Openly resist or refuse to obey" , "Withstand" .)