Catch in the act (3)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">catch in the act</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for nab that I've seen before include "Catch; grab suddenly" , "Cop" , "Capture, catch" , "Pinch" , "Apprehend" .)