A game of pool, possibly (4)
I believe the answer is:
polo
'a game' is the definition.
(polo is a kind of game)
'pool possibly' is the wordplay.
'possibly' indicates anagramming the letters.
'pool' is an anagram of 'POLO'.
'of' acts as a link.
(Other definitions for polo that I've seen before include "Game - explorer - mint - VW" , "Ball game played on horseback" , "It's played in water and on horseback" , "Game on horseback or in water" , "Horse-game played with loop" .)