More rioting by American claiming negative response is monumental (8)
I believe the answer is:
enormous
'monumental' is the definition.
(thesaurus)
'more rioting by american claiming negative response' is the wordplay.
'rioting' indicates an anagram.
'by' is a charade indicator (letters next to each other).
'american' becomes 'us' (abbreviation for United States).
'claiming' indicates putting letters inside.
'negative response' becomes 'no' (I've seen this in other clues).
'more' anagrammed gives '[more]'.
'[more]'+'us'='ermous'
'ermous' placed around 'no' is 'ENORMOUS'.
'is' is the link.
(Other definitions for enormous that I've seen before include "Fat" , "Colossal, huge" , "Gross" , "Extraordinarily large" , "Extremely large" .)