Agitated doubter to butt in (7)
I believe the answer is:
obtrude
'butt in' is the definition.
(I've seen this in another clue)
'agitated doubter' is the wordplay.
'agitated' indicates an anagram.
'doubter' anagrammed gives 'OBTRUDE'.
'to' is the link.
(Other definitions for obtrude that I've seen before include "Be offensively prominent" , "Thrust oneself forward" , "Become unwelcomely prominent" , "Interfere" , "Make unpleasantly noticeable" .)