Game of pool? For sure! (9)
I believe the answer is:
foolproof
'sure' is the definition.
('foolproof' can be a synonym of 'sure')
'game of pool? for' is the wordplay.
'game' indicates anagramming the letters (solving anagrams is a game).
'of'+'pool'+'for'='ofpoolfor'
'ofpoolfor' anagrammed gives 'FOOLPROOF'.
(Other definitions for foolproof that I've seen before include "Completely safe" , "Certain" , "Not admitting failure" , "Not liable to failure" , "incapable of going wrong" .)