Riot Act changes getting Yard in outrage (8)
I believe the answer is:
atrocity
'outrage' is the definition.
(I've seen this before)
'riot act changes getting yard' is the wordplay.
'changes' is an anagram indicator.
'getting' means one lot of letters go next to another.
'yard' becomes 'y' (abbreviation).
'riot'+'act'='riotact'
'riotact' anagrammed gives 'atrocit'.
'atrocit'+'y'='ATROCITY'
'in' acts as a link.
(Other definitions for atrocity that I've seen before include "Barbarous, inhuman act" , "Appalling act" , "Wickedness" , "'Barbarity, heinous act (8)'" , "Frightful act of citatory kind" .)