Appearing at the centre with a revolutionary complaint (7)
I believe the answer is:
earache
'complaint' is the definition.
(a type of medical complaint)
'appearing at the centre with a revolutionary' is the wordplay.
'at the centre' says to take the centre.
'with' is a charade indicator (letters next to each other).
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
The middle of 'appearing' is 'ear'.
'ear'+'a'+'che'='EARACHE'
(Other definitions for earache that I've seen before include "Pain in an aural appendage" , "Pain in aural organ" , "minor complaint" , "complaint to The Listener" , "Pain inside the head" .)