Ready to ring pub about game (6)
I believe the answer is:
tennis
'game' is the definition.
(tennis is a game)
'ready to ring pub about' is the wordplay.
'ready to' becomes 'set' (synonyms).
'ring' is an insertion indicator.
'pub' becomes 'inn' (an inn is a type of pub).
'about' says the letters should be written backwards.
'set' placed around 'inn' is 'sinnet'.
'sinnet' reversed gives 'TENNIS'.
(Other definitions for tennis that I've seen before include "Table -, - elbow" , "McEnroe's game" , "Sent in (anag.)" , "Game played on court" , "Game (where love is nought?)" .)