Lots upset after vicar renounces allegiance (7)
I believe the answer is:
revolts
'renounces allegiance' is the definition.
(revolting is a kind of renouncing allegiance)
'lots upset after vicar' is the wordplay.
'upset' indicates anagramming the letters.
'after' means one lot of letters go next to another.
'vicar' becomes 'rev' (short for reverend).
'lots' anagrammed gives 'olts'.
'olts' after 'rev' is 'REVOLTS'.
(Other definitions for revolts that I've seen before include "Rebels" , "Acts of defiance" , "Disgusts" .)