Bobbed down (6)
I believe the answer is:
ducked
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">bobbed down</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 ducked that I've seen before include "Bowed head to avoid missile" , "Went down" , "was plunger?" , "Dipped" , "Avoided as mallard might" .)