Show mode off (4)
I believe the answer is:
demo
'show' is the definition.
(I've seen this before)
'mode off' is the wordplay.
'off' is an anagram indicator.
'mode' is an anagram of 'DEMO'.
(Other definitions for demo that I've seen before include "Tape sent to recording studio" , "March (abbr)" , "Protest march (sl.)" , "Protest (abbr)" , "exhibit" .)