Show discharge when back is scratched (4)
I believe the answer is:
demo
'show' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for demo that I've seen before include "March (abbr)" , "Eg, protest march" , "Protest (abbr)" , "Political protest" , "Tape sent to recording studio" .)