...s game (5)
I believe the answer is:
fives
'game' is the definition.
(fives is a kind of game)
's' is the wordplay.
I cannot quite see how this works, but
's' could be 'es' (the letter S can be spelt es) and 'es' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for fives that I've seen before include "Small numbers" , "Game similar to squash" , "horse disease as before" , "Indoor court game" , "Squash relative" .)