Real idiot upset leader (9)
I believe the answer is:
editorial
'leader' is the definition.
(type of newspaper article)
'real idiot upset' is the wordplay.
'upset' is an anagram indicator.
'real'+'idiot'='realidiot'
'realidiot' anagrammed gives 'EDITORIAL'.
(Other definitions for editorial that I've seen before include "(Paper's) leader" , "Chief newspaper article" , "Newspaper article - "I led a riot" (anag)" , "matter of opinion" , "Article giving a newspaper's opinion" .)