Go up against
I believe the answer is:
oppose
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">go up against</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 oppose that I've seen before include "Argue against" , "Resist, go against" , "Take stand against, resist" , "Actively resist" , "Counter" .)