Reveal part of NI to be in confrontation (8)
I believe the answer is:
showdown
'confrontation' is the definition.
(I know that confrontation can be written as showdown)
'reveal part of ni' is the wordplay.
'reveal' becomes 'show' (synonyms).
'part of ni' becomes 'down' (County Down, part of Northern Ireland).
'show'+'down'='SHOWDOWN'
'to be in' is the link.
(Other definitions for showdown that I've seen before include "Final confrontation as in western film" , "Decisive confrontation" , "Denouement" , "Climactic finale" , "Dramatic conclusion" .)