Card game players holding an ace (7)
I believe the answer is:
canasta
'card game' is the definition.
(canasta is a kind of card game)
'players holding an ace' is the wordplay.
'players' becomes 'cast' (group of actors).
'holding' indicates putting letters inside.
'ace' becomes 'a' (abbreviation).
'cast' going around 'an' is 'canast'.
'canast'+'a'='CANASTA'
(Other definitions for canasta that I've seen before include "Rummy-like card-game" , "Form of rummy using two decks of cards and four jokers" , "Card game at a scan" , "Card game like rummy" , "this needs two packs" .)