Water polo maybe (4)
I believe the answer is:
pool
'water' is the definition.
(pool is a kind of water)
'polo maybe' is the wordplay.
'maybe' indicates anagramming the letters.
'polo' is an anagram of 'POOL'.
(Other definitions for pool that I've seen before include "American game resembling snooker" , "found in watery location" , "Ball game - small body of water" , "Puddle - game with balls" , "Put in common fund; (pub) game" .)