Moderated bad temper displayed in commercial (6)
I believe the answer is:
abated
'moderated' is the definition.
(abate can mean to moderate or diminish)
'bad temper displayed in commercial' is the wordplay.
'bad temper' becomes 'bate' (old-fashioned slang for a bad mood).
'displayed in' indicates putting letters inside.
'commercial' becomes 'ad' (abbreviation for advertisement).
'bate' placed within 'ad' is 'ABATED'.
(Other definitions for abated that I've seen before include "Slackened off, died back" , "Eased" , "grew less" , "Diminished" , "Became less intense" .)