Head of state against appearing in parade (7)
I believe the answer is:
monarch
'head of state' is the definition.
(monarch is a type of head of state)
'against appearing in parade' is the wordplay.
'against' becomes 'on' (on can mean by or up against).
'appearing in' is an insertion indicator.
'parade' becomes 'march' (a ceremonial march).
'on' put inside 'march' is 'MONARCH'.
(Other definitions for monarch that I've seen before include "Sovereign; butterfly" , "Butterfly (emperor, say?)" , "one over realm?" , "King or butterfly" , "Head of State" .)