Mild anger over spilled tea (9)
I believe the answer is:
temperate
'mild' is the definition.
('temperate' can be similar in meaning to 'mild')
'anger over spilled tea' is the wordplay.
'anger' becomes 'temper' (temper is a kind of anger**).
'over' says to put letters next to each other.
'spilled' indicates an anagram.
'tea' anagrammed gives 'ate'.
'temper'+'ate'='TEMPERATE'
(Other definitions for temperate that I've seen before include "with balmy climate" , "pleasant" , "Restrained" , "Abstemious" , "even" .)