Upset surrounding pub game (6)
I believe the answer is:
tennis
'upset surrounding pub game' is the definition.
'tennis' can be an answer for 'game' (tennis is a game). I am not certain of the 'upset surrounding pub' bit.
'upset surrounding pub game' is the wordplay.
'upset' shows that the letters should be reversed in order.
'surrounding' means one lot of letters goes inside another.
'pub' becomes 'inn' (an inn is a type of pub).
'game' becomes 'set' (I can't explain this - if you can you should believe this answer much more).
'inn' going inside 'set' is 'sinnet'.
'sinnet' in reverse letter order is 'TENNIS'.
Can you help me to learn more?
(Other definitions for tennis that I've seen before include "Sent in (anag.)" , "Evil trap set up for game" , "Game that depends on service" , "Popular racquet game - anyone for it?" , "Wimbledon sport" .)