Protesting vigorously (2,2,4)
I believe the answer is:
up in arms
'protesting vigorously' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for up in arms that I've seen before include "Protesting strongly" , "Rioting" , "Protesting vigorously, in militant mood" , "Protesting vigorously, ready for fight" , "Indignant" .)