Lead part, so got in cast (11)
I believe the answer is:
protagonist
'lead' is the definition.
(thesaurus)
'part so got in cast' is the wordplay.
'cast' indicates an anagram (letters are dispersed or cast around).
'part'+'so'+'got'+'in'='partsogotin'
'partsogotin' is an anagram of 'PROTAGONIST'.
(Other definitions for protagonist that I've seen before include "Leading character in a play, novel, etc" , "Hero" , "Leading player" , "Chief character in a story" , "Advocate" .)