As Mr. Black had explained, the magic circle limited everyone within it therefore making pulling a man's head off a pipe dream for most people. It was only possible if the perpetrator possessed a high level of inborn power or innate strength.
Another possibility was a creature or warrior of high rank, at the Sky Realm or Void Realm, making a move. This was because the formation gradually lost its effects the stronger someone was. However, let alone Sky Realm and Void Realm warriors, even Earth Realm warriors and creatures were very rare. Additionally, while the formation could not perfectly restrict stronger warriors and creatures, it had a detection system that could recognize those above a certain level of power. That way, if they used their high level abilities within the town, a similarly strong town official or soldier could be sent to deal with them.
