Moving swiftly (6)
I believe the answer is:
racing
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">moving swiftly</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for racing that I've seen before include "Dashing" , "going very fast" , "Sport; moving swiftly" , "The sport of kings" , "Running fast" .)