Advice on kids fighting

I live in an apartment complex. there is a kid that comes around and physically attacks other kids. one day it was a headlock then, it escalated to punching in the face. A neighbor was beaten and bloody. he even threatened to hit my kid with a chair. these are 8 year olds! I went and spoke to the mother but, she was very aggressive and didn't seem very concerned. (I see where he gets it from) The next time this happens, should I just call the police?