Equestrian's control
I believe the answer is:
rein
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">equestrian's control</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 rein that I've seen before include "one's attached to a bit" , "Restraint; strap attached to horse's bit" , "Controlling strap" , "Part of tack" , "Director's power" .)