Be against (6)
I believe the answer is:
oppose
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">be against</span>' is the definition.<br/ ><span class="explanation-format__explanation">(synonyms)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for oppose that I've seen before include "Resist, be hostile to" , "Resist, contend with" , "Act against" , "Counter" , "Refute - confront" .)