Story editor backed up report (9)
I believe the answer is:
accounted
'backed up report' is the definition.
The definition and answer can be both to do with ownership as well as being past participle verbs.
Perhaps there's a link between them I don't understand?
'story editor' is the wordplay.
'story' becomes 'account' ('account' can be a synonym of 'story').
'editor' becomes 'ed'.
'account'+'ed'='ACCOUNTED'
Can you help me to learn more?
(Another definition for accounted that I've seen is " Answered".)