Back in a game (3)
I believe the answer is:
ago
'back' is the definition.
('years back' means 'years ago')
'a game' is the wordplay.
'game' becomes 'go game' (go is a board game).
'a'+'go'='AGO'
'in' is the link.
(Other definitions for ago that I've seen before include "Previously" , "Earlier, gone by" , "In past times" , "Gone, past, since" , "(Years) before the present time" .)