Set an ambush (3,2,4)
I believe the answer is:
lie in wait
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">set an ambush</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 lie in wait that I've seen before include "prepare a trap" , "Prepare to attack" , "Hope to catch" , "remain hidden while preparing to attack" , "hover" .)