Thwart; obstruct (6)
I believe the answer is:
stymie
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">thwart</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">obstruct</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I know that obstruct can be written as stymie)</span><br/ ><br/ ></span>
(Other definitions for stymie that I've seen before include "Old putting problem" , "Obstruction (originally at golf)" , "'Hinder, obstruct (6)'" , "Block or thwart, say a golf putt" , "Tricky situation" .)