Article about riot appeared (6)
I believe the answer is:
arisen
'appeared' is the definition.
(arise can mean to appear or crop up)
'article about riot' is the wordplay.
'article' becomes 'an' (indefinite article).
'about' means one lot of letters goes inside another.
'riot' becomes 'rise' (riot can mean to rise up).
'an' going around 'rise' is 'ARISEN'.
(Other definitions for arisen that I've seen before include "(Has) come into view; (has) originated (from)" , "Come to light" , "It's appeared" , "Up on the rocks" , "(Having) occurred" .)