Justified, conflict with editor following angry tirade (9)
I believe the answer is:
warranted
'justified' is the definition.
('warrant' can be a synonym of 'justify')
'conflict with editor following angry tirade' is the wordplay.
'conflict' becomes 'war' (war is a kind of conflict).
'with' means one lot of letters go next to another.
'editor' becomes 'ed'.
'following' says to put letters next to each other.
'angry tirade' becomes 'rant' (I've seen this before).
'ed' after 'rant' is 'ranted'.
'war'+'ranted' is 'WARRANTED'.
(Another definition for warranted that I've seen is " Justified or guaranteed".)