Moderate display of anger (6)
I believe the answer is:
temper
This clue is a double definition.
'moderate' is the first definition.
('temper' can be a synonym of 'moderate')
'display of anger' is the second definition.
(I've seen this before)
(Other definitions for temper that I've seen before include "Moderate; ill humour" , "Harden using heat" , "Tendency to anger" , "Adjust" , "Mood, maybe angry" .)