A name adopted by players before a game (7)
I believe the answer is:
canasta
'game' is the definition.
(canasta is a kind of game)
'a name adopted by players before a' is the wordplay.
'name' becomes 'n' (common abbreviation e.g. on forms).
'adopted by' means one lot of letters goes inside another (I've seen this in other clues).
'players' becomes 'cast' (I've seen this before**).
'before' is a charade indicator (letters next to each other).
'a'+'n'='an'
'an' inserted into 'cast' is 'canast'.
'canast'+'a'='CANASTA'
(Other definitions for canasta that I've seen before include "Card-game, a form of rummy" , "Game played with two packs of cards and jokers" , "Card game at a scan" , "Decorated with artificial jewels" , "Card game of the rummy family" .)