Protesting hotly (2,2,4)
I believe the answer is:
up in arms
'protesting hotly' 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 "Openly protesting" , "Protesting vigorously, in militant mood" , "Outraged" , "Protesting vociferously" , "Protesting angrily - with weapons aloft?" .)