Parade's backer opening case (5)
I believe the answer is:
event
'case' is the definition.
(I know that case can be written as event)
'parade's backer opening' is the wordplay.
'parade's backer' becomes 'e' (I can't justify this - if you can you should give a lot more credence to this answer).
'opening' becomes 'vent' (vent is a kind of opening).
'e'+'vent'='EVENT'
Can you help me to learn more?
(Other definitions for event that I've seen before include "Fixture" , "Occurren" , "Incident, occurrence" , "riding competition" , "tournament" .)