Protest about mean rotters (11)
I believe the answer is:
remonstrate
'protest' is the definition.
(I've seen this before)
'about mean rotters' is the wordplay.
'about' indicates an anagram.
'mean'+'rotters'='meanrotters'
'meanrotters' with letters rearranged gives 'REMONSTRATE'.
(Other definitions for remonstrate that I've seen before include "Argue in protest" , "Make a forceful protest" , "Argue fiercely" , "Make a forcefully reproachful protest" , "Take exception to" .)