Following retirement, group takes over pub game (6)
I believe the answer is:
tennis
'game' is the definition.
(tennis is a kind of game)
'following retirement group takes over pub' is the wordplay.
'following retirement' says the letters should be written backwards (retire can mean to go back).
'group' becomes 'set' (both can mean a collection).
'takes over' means one lot of letters goes inside another.
'pub' becomes 'inn' (an inn is a type of pub).
'set' going around 'inn' is 'sinnet'.
'sinnet' in reverse letter order is 'TENNIS'.
(Other definitions for tennis that I've seen before include "Racquet sport" , "Game, orig. sphairistike" , "Wimbledon sport" , "Racket sport" , "Net sport" .)