Performing arts supremo (4)
I believe the answer is:
tsar
'supremo' is the definition.
(I've seen this before)
'performing arts' is the wordplay.
'performing' is an anagram indicator.
'arts' anagrammed gives 'TSAR'.
(Other definitions for tsar that I've seen before include "Absolute ruler" , "Star for a Russian emperor" , "Alexander and Nicholas held this title in Russia" , "specific authority" , "Old Russian ruler" .)