Card player's first to put up stakes (7)
I believe the answer is:
jackpot
'stakes' is the definition.
(jackpot is a kind of stakes)
'card player's first to put up' is the wordplay.
'card' becomes 'jack' (type of playing card).
'player's first' becomes 'p' (1st letter of 'player').
'put up' says the letters should be written backwards.
'to' in reverse letter order is 'ot'.
'jack'+'p'+'ot'='JACKPOT'
(Other definitions for jackpot that I've seen before include "best prize!" , "pool" , "First prize" , "Huge gambling prize" , "Great thing to hit?" .)