Form of protest (3-2)
I believe the answer is:
sit-in
'form of protest' is the definition.
(I know that sit-in is a type of demonstration)
This is the entire clue.
(Other definitions for sit-in that I've seen before include "Type of demo" , "Act of civil disobedience" , "Occupation of a place as a protest" , "Form of civil disobedience" , "Occupation of building as form of protest" .)