Cardinal's displeasure at court summons originally is diverting (9)

'is diverting' is the definition.
(to redirect is to divert elsewhere)

'cardinal's displeasure at court summons originally' is the wordplay.
'cardinal' becomes 'red' (cardinal is a shade of red).
'displeasure' becomes 'ire' (I've seen this in another clue).
'at' is a charade indicator (letters next to each other).
'court summons originally' becomes 'cts' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'red'+'ire'+'cts'='REDIRECTS'