For a threat to be a valid breach of the Legal Principle, it needs to be substantial and imminent.
When a substantial threat is imminent, the person at risk is always legally entitled self-defence; utilizing the least amount of force necessary to terminate that threat.
Local community must determine the threshold of imminence
What exactly constitutes ‘substantial’ and ‘imminent’ are both subjective grey-areas, and must be decided by the local community. This definition will continue to evolve as each new case sets a legal precedent. There already exists a vast history of legal cases that can inform proper judgement.