Behead bears? Not us (6)
I believe the answer is:
others
'not us' is the definition.
(I've seen this in another clue)
I don't understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for others that I've seen before include "Certainly not us" , "Not the same one already mentioned" , "He rots (anag.)" , "People in throes - not us" , "Different ones" .)