Irregular soldier (9)
I believe the answer is:
guerrilla
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">irregular soldier</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 guerrilla that I've seen before include "political insurgent" , "Underground fighter" , "Resistance fighter" , "Combatant" , "freedom fighter?" .)