Since entering, can’t get a game (7)
I believe the answer is:
canasta
'game' is the definition.
(canasta is a kind of game)
'since entering can't get a' is the wordplay.
'since' becomes 'as' (I've seen this in other clues).
'entering' means one lot of letters goes inside another.
'get' means one lot of letters go next to another.
'as' placed into 'cant' is 'canast'.
'canast'+'a'='CANASTA'
(Other definitions for canasta that I've seen before include "Two-pack card game" , "Game played with two packs of cards and jokers" , "Rummy-like card-game" , "Card game of the rummy family" , "Form of rummy using two decks of cards and four jokers" .)