Open rebellion (6)
I believe the answer is:
mutiny
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">open rebellion</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for mutiny that I've seen before include "Revolt against authority" , "Military rebellion" , "Open rebellion against constituted authority" , "Rising, rebellion" , "Insurrection" .)