Come in and upset authority (9)
I believe the answer is:
dominance
'authority' is the definition.
('dominance' can be a synonym of 'authority')
'come in and upset' is the wordplay.
'upset' is an anagram indicator.
'come'+'in'+'and'='comeinand'
'comeinand' with letters rearranged gives 'DOMINANCE'.
(Other definitions for dominance that I've seen before include "Supremacy" , "top position" , "Commanding position" , "Influence (over others)" , "Ascendancy" .)