Mallet game (4)
I believe the answer is:
polo
'mallet game' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for polo that I've seen before include "In which horsemen attack and defend" , "Team game played with horses" , "Game; Italian explorer" , "Hockey on horseback" , "explorer of the thirteenth century" .)