Some comedian backed protest (4)
I believe the answer is:
demo
'protest' is the definition.
(I've seen this before)
'some comedian backed' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'backed' says the letters should be written backwards.
'omed' is hidden in the letters of 'comedian'.
'omed' reversed gives 'DEMO'.
(Other definitions for demo that I've seen before include "Protest march (sl.)" , "March (abbr)" , "Public protest meeting" , "Protest (abbr)" , "presentation" .)