ANBU aren't police but the hand of the Kage meant to dispatch missing nin and dangerous people without causing too much ruckus. Hence the masks and assassin training. A ninja of the village is responding to a possible situation. If they think he's got it under control, why complicate matters more?
Also, the ninja are the military. Everyone one of them from genin to kage. They all have some level of authority as peace keepers in their own village and they in turn had a police system with the uchiha but i don't know if that even exists in this AU of Konoha
Brad is a part of said military and chose to fight in a secluded area, outside of the villages walls on agreed upon terms.
Also, Geo is the NPC pool in this game what he responds to is up to him.
In my understanding of the context, many foreign nin would be in Konoha and mercs have been killing cross communication with the hidden villages. The ANBU are out to prevent said mercs from killing messengers or attacking the village. Also the villages don't all get along, so some of that may be to prevent random fighting within the walls of the city.
Outside the walls, I do agree, let them have at it. So yeah, you win!