Ride fast (6)
I believe the answer is:
gallop
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">ride fast</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 gallop that I've seen before include "Horse's fastest pace" , "Horse's gait" , "Hurry (on horseback?)" , "Fast speed of horse" , "Fast ride" .)