Lumps express disagreement, reportedly, with prearranged combats (7)
I believe the answer is:
nodules
'lumps' is the definition.
(a nodule is a lump of cells in the body)
I cannot understand how the remainder of the clue works.
Can you help me to learn more?
(Other definitions for nodules that I've seen before include "Loudens like lumps" , "Small rounded lumps" , "Loudens due to small lumps" , "Small swellings" , "Small lumps - led us on (anag)" .)