A game of wits (7)
I believe the answer is:
marbles
This clue is a double definition.
'a game' is the first definition.
(I know that marbles is a type of child\\u0027s game)
'wits' is the second definition.
(marbles can informally mean wits or sanity)
'of' is the link.
(Other definitions for marbles that I've seen before include "Mind" , "Small spheres of glass - statuary" , "Glass balls to play with" , "Children's game played with little balls" , "You'll be mad if you lose them" .)