Tennis player's good service (4)
I believe the answer is:
graf
'tennis player's' is the definition.
(graf was a tennis player)
'good service' is the wordplay.
'good' becomes 'g' (abbreviation).
'service' becomes 'raf'.
'g'+'raf'='GRAF'
(Other definitions for graf that I've seen before include "Noted tennis player" , "Seven-times women's Wimbledon champion, b. 1969" , "German tennis player, b. 1969" , "German count - German tennis player" , "Steffi --, tennis champion" .)