Assumptions of the man surrounded by right-wingers (8)
I believe the answer is:
theories
'assumptions' is the definition.
(a theory is an assumption or conjecture)
'the man surrounded by right-wingers' is the wordplay.
'the man' becomes 'he' (pronoun for a man).
'surrounded by' is an insertion indicator.
'right-wingers' becomes 'tories' (Tory is an example).
'he' placed within 'tories' is 'THEORIES'.
'of' acts as a link.
(Other definitions for theories that I've seen before include "Assumptions" , "premises?" , "Abstract principles" , "Ideas or suppositions" , "Set of principles on which practices are based" .)