Completely stump (6)
I believe the answer is:
stymie
'completely stump' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for stymie that I've seen before include "Block or obstruct as in golf (6)" , "Block or thwart, as on golf course" , "Hinder, obstruct, thwart" , "Block the path of, as on golf green" , "balk" .)