Moderation in anger over social event not starting (10)
I believe the answer is:
temperance
'moderation' is the definition.
(I know that moderation can be written as temperance)
'anger over social event not starting' is the wordplay.
'anger' becomes 'temper' (temper is a kind of anger).
'over' is a charade indicator (letters next to each other) (in a down clue, some letters go over others).
'social event' becomes 'dance' (a dance is a type of social event).
'not starting' means to remove the first letter.
'dance' with its first letter taken off is 'ance'.
'temper'+'ance'='TEMPERANCE'
'in' is the link.
(Other definitions for temperance that I've seen before include "Abstinence from alcohol" , "virtue?" , "for staying off drink" , "Moderation" , "Feature of traditional Methodism" .)