Engaged in litigation (4)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">engaged in litigation</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 sued that I've seen before include "Took legal action against" , "taken to court" , "Prosecuted" , "Brought an action against" , "Started legal proceedings against (someone)" .)