What does the cryptic crossword clue "Protest involving mean rotters (11)" mean?

The definition is "Protest". The wordplay uses an anagram. anagram of MEAN + ROTTERS = REMONSTRATE; definition: "Protest" The answer is REMONSTRATE.

Protest involving mean rotters (11)

Guardian Cryptic #23780 | 25 Across | 2006-05-31 flower