Like an exclusive group in confrontation outside pub after upset (8)
I believe the answer is:
clannish
'like an exclusive group' is the definition.
'confrontation outside pub after upset' is the wordplay.
'confrontation' becomes 'clash'.
'outside' is an insertion indicator.
'pub' becomes 'inn' (I've seen this before).
'after upset' shows that the letters should be reversed in order (in a down clue, letters go up).
'inn' backwards is 'nni'.
'clash' placed around 'nni' is 'CLANNISH'.
'in' is the link.
(Other definitions for clannish that I've seen before include "Excluding non-group members" , "Excluding others outside one's own group" , "Sticking to one group" , "Tribal" , "Tending to exclude those outside the group" .)