Devils protected by rude monsters (6)
I believe the answer is:
demons
'devils' is the definition.
('demon' can be a synonym of 'devil')
'protected by rude monsters' is the wordplay.
'protected by' indicates a hidden word.
'DEMONS' is hidden in the letters of 'rude monsters'.
(Other definitions for demons that I've seen before include "Evil supernatural beings" , "Wicked people" , "Fiends or devils" , "Evil spirits, devils" .)