Master versus riotous assembly? (8)
I believe the answer is:
virtuoso
'master' is the definition.
(thesaurus)
'versus riotous assembly?' is the wordplay.
'versus' becomes 'v'.
'assembly?' is an anagram indicator (I've seen 'assembly' mean this).
'riotous' anagrammed gives 'irtuoso'.
'v'+'irtuoso'='VIRTUOSO'
(Other definitions for virtuoso that I've seen before include "Highly skilled musician" , "Brilliant -- prodigy" , "Musician who's dazzlingly skilled" , "Musician with exceptional technique" , "Great player" .)