Mind game? (7)
I believe the answer is:
marbles
I believe this is a double definition.
'mind' is the first definition.
(I've seen this before)
'game?' is the second definition.
(marbles is a kind of game)
(Other definitions for marbles that I've seen before include "You'll be mad if you lose them" , "Glass balls to play with" , "Small spheres of glass - statuary" , "Mind" , "alleys, perhaps" .)