Call into question (9)
I believe the answer is:
challenge
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">call into question</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for challenge that I've seen before include "Object to" , "Question truth of - dare" , "difficulty" , "Invitation to contest" , "call for proof" .)