Our rivals with old blood-feud, primarily (3,3)
I believe the answer is:
the mob
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for the mob that I've seen before include "common people" , "lot to which 20 [JAMES GANDOLFINI] in character belonged" , "Organised criminals" , "gangsters" .)