Irregular role at home around South America (8)
I believe the answer is:
partisan
'irregular' is the definition.
('partisan' can be similar in meaning to 'irregular')
'role at home around south america' is the wordplay.
'role' becomes 'part' ('part' can be a synonym of 'role').
'at home' becomes 'in' ('in' can be similar in meaning to 'at home').
'around' is an insertion indicator.
'south' becomes 's' ('S' can be a synonym of 'south').
'america' becomes 'a' (common abbreviation - e.g. in organisation names).
's'+'a'='sa'
'in' placed around 'sa' is 'isan'.
'part'+'isan'='PARTISAN'
(Other definitions for partisan that I've seen before include "Unquestioning supporter -- aspirant (anag)" , "Strongly supporting one side" , "Strong party supporter" , "Adherent" , "Prejudiced towards one side" .)