Clearly in an imperfect world some people will initiate force against others. The judiciary's role is to decide if this has occurred, and what level of defensive force and retaliatory force is appropriate when it has.
Clearly some of these roles must be carried out by the police (where short-term responses are required), and by the government in setting guidelines for the judiciary.
Like the police force, the judiciary generally makes decisions on internal matters - which occur within the area of their government.
See