Game: if lost, it would make you mad? (7)
I believe the answer is:
marbles
I believe this clue is a double definition.
'game' is the first definition.
(I know that marbles is a type of child\\u0027s game)
'if lost it would make you mad?' is the second definition.
(to lose one's marbles is to go mad)
(Other definitions for marbles that I've seen before include "Small balls of coloured glass" , "Small spheres of glass - statuary" , "Children's game played with little balls" , "Mind" , "Glass balls to play with" .)