Irishman with anger about appearing in supporting role (9)
I believe the answer is:
patronage
'supporting role' is the definition.
(I've seen this before)
'irishman with anger about appearing' is the wordplay.
'irishman' becomes 'pat'.
'with' says to put letters next to each other.
'anger' becomes 'rage' (rage is a kind of anger**).
'about' is an insertion indicator.
'appearing' becomes 'on' (e.g. on stage or on television).
'rage' placed around 'on' is 'ronage'.
'pat'+'ronage'='PATRONAGE'
'in' acts as a link.
(Other definitions for patronage that I've seen before include "Sponsorship - condescending manner" , "supporting role" , "financial backing" , "Regular custom" , "The power to control privileges" .)