Create a brief act to be performed (9)
I believe the answer is:
fabricate
'create' is the definition.
(thesaurus)
'a brief act to be performed' is the wordplay.
'to be performed' indicates anagramming the letters (I've seen 'is performed' mean this).
'a'+'brief'+'act'='abriefact'
'abriefact' is an anagram of 'FABRICATE'.
(Other definitions for fabricate that I've seen before include "Invent, make up" , "Construct or invent" , "forge" , "Invent or manufacture a story" , "Make up; manufacture" .)