Group outside tavern turned up for a game (6)
I believe the answer is:
tennis
'a game' is the definition.
(tennis is a kind of game)
'group outside tavern turned up' is the wordplay.
'group' becomes 'set' (set is a kind of group).
'outside' indicates putting letters inside.
'tavern' becomes 'inn' (I've seen this before).
'turned up' shows that the letters should be reversed in order.
'set' going around 'inn' is 'sinnet'.
'sinnet' written backwards gives 'TENNIS'.
'for' acts as a link.
(Other definitions for tennis that I've seen before include "Henman's game" , "Pete Sampras's game" , "Court-based sport" , "Sent in (anag.)" , "Sent in, strangely, for sport" .)