Revolutionary left nine out (5)
I believe the answer is:
lenin
'revolutionary' is the definition.
(I've seen this before)
'left nine out' is the wordplay.
'left' becomes 'l' (common abbreviation).
'out' indicates anagramming the letters (out can mean wrong or inaccurate).
'nine' with letters rearranged gives 'enin'.
'l'+'enin'='LENIN'
(Other definitions for lenin that I've seen before include "First Soviet leader" , "Soviet Union's first premier" , "V. I. -, Soviet politician and revolutionary" , "Communist leader" , "Marxist theoretician" .)