Conjecture from man interrupting person in party (6)
I believe the answer is:
theory
'conjecture' is the definition.
(I've seen this in another clue)
'man interrupting person in party' is the wordplay.
'man' becomes 'he' (he refers to a man).
'interrupting' indicates putting letters inside.
'person in party' becomes 'Tory' (member of the Conservative Party).
'he' going within 'tory' is 'THEORY'.
'from' is the link.
(Other definitions for theory that I've seen before include "Explanation or system of anything" , "Hypothesis, thesis" , "Set of ideas formed from reasoning" , "Opinion or supposition to explain something" , "Abstract explanation" .)