After a couple of drinks, setter’s game! (3,5)
I believe the answer is:
gin rummy
'setter's game' is the definition.
'gin rummy' can be an answer for 'game' (gin rummy is a kind of game). I am unsure of the 'setter's' bit.
'after a couple of drinks' is the wordplay.
'a couple of drinks' means two replacements for 'drink'.
'after' says to put letters next to each other.
'drink' becomes 'gin' (gin is a kind of drink).
'drink' becomes 'rummy' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'gin' put next to 'rummy' is 'GIN RUMMY'.
Can you help me to learn more?
(Other definitions for gin rummy that I've seen before include "cards" , "Card game" .)