A leader in revolutionary arts (4)
I believe the answer is:
star
'a leader' is the definition.
(thesaurus)
'revolutionary arts' is the wordplay.
'revolutionary' indicates an anagram.
'arts' anagrammed gives 'STAR'.
'in' acts as a link.
(Other definitions for star that I've seen before include "Big name" , "Cult sci-fi film" , "It twinkles" , "personality?" , "Eg, Antares" .)