Battle against (6)
I believe the answer is:
combat
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">battle 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 combat that I've seen before include "Fight - strive against" , "Armed fighting" , "Conflict" , "Fight or contest, may be mortal" , "Take action to deal with - fight" .)