Maybe criminal group fights here (4)
I believe the answer is:
ring
This clue is a double definition.
'maybe criminal group' is the first definition.
(ring can mean a criminal gang)
'fights here' is the second definition.
(boxing ring)
(Other definitions for ring that I've seen before include "Surround; reverberate" , "Call - cartel" , "Frodo's burden (Tolkien)" , "Chime" , "Phone; circular band" .)