Game that's a variation of polo (4)
I believe the answer is:
pool
'game' is the definition.
(I know that pool is a type of table game)
'variation of polo' is the wordplay.
'variation of' indicates an anagram (I've seen 'variations' mean this).
'polo' anagrammed gives 'POOL'.
'that's a' acts as a link.
(Other definitions for pool that I've seen before include "17 - small stretch of water" , "stakes" , "Put into common fund for sharing" , "Game played on a table with six pockets" , "Shared supply; game" .)