Game played after love letter (5)
I believe the answer is:
omega
'letter' is the definition.
(omega is a kind of letter)
'game played after love' is the wordplay.
'played' indicates an anagram.
'after' is a charade indicator (letters next to each other).
'love' becomes 'o' (In tennis, 'love' means 'zero').
'game' with letters rearranged gives 'mega'.
'mega' put after 'o' is 'OMEGA'.
(Other definitions for omega that I've seen before include "completes a series" , "24th Greek letter" , "Last thing" , "Greek character symbolizing resistance" , "character from Athens" .)