Score with ace in card game (6-3)
I believe the answer is:
twenty-one
'card game' is the definition.
(twenty-one is a kind of card game)
'score with ace' is the wordplay.
'score' becomes 'twenty' ('twenty' can be a synonym of 'score'**).
'with' means one lot of letters go next to another.
'ace' becomes 'one' ('one' can be a synonym of 'ace').
'twenty'+'one'='TWENTY-ONE'
'in' acts as a link.
(Other definitions for twenty-one that I've seen before include "Target total in blackjack or pontoon" , "Card game, blackjack or pontoon" , "XXI - used to be the coming of age year" .)