Moorish sailor's card game (9)
I believe the answer is:
Here is my best explanation:
'card game' is the definition.
(blackjack is a kind of card game)
'moorish sailor's' is the wordplay.
'moorish' becomes 'black'.
'sailor' becomes 'jack' (I've seen this before).
(Other definitions for blackjack that I've seen before include "Vingt-et-un - pirates' ensign", "Card game", "Gambling card game", "Casino card game", "club", "A card game in which the object is to beat the bank", "Club" and "2 8 [CASINO GAME]".)