Anger following Caesar's greeting? That's mean, perhaps (7)
I believe the answer is:
average
'that's mean perhaps' is the definition.
(mean is a kind of average)
'anger following caesar's greeting?' is the wordplay.
'anger' becomes 'rage' (rage is a kind of anger).
'following' says to put letters next to each other.
'caesar's greeting?' becomes 'ave' (I've seen this in another clue).
'rage' put after 'ave' is 'AVERAGE'.
(Other definitions for average that I've seen before include "Mean - typical" , "Mean, median or middling" , "Mean - norm" , "Normal; mean" , "Mediocre, commonplace" .)