Game played on horseback (4)
I believe the answer is:
polo
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">game played on horseback</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 polo that I've seen before include "Game; Venetian explorer" , "car?" , "It's played in water and on horseback" , "In which horsemen attack and defend" , "Sport - mint - explorer" .)