In which situation is it acceptable for a security guard to detain an individual?

Detaining an individual is a significant action that security guards must take with caution and in accordance with the law. The correct answer is when a security guard witnesses a crime. In this context, witnessing a crime provides the legal justification for detaining an individual. Security guards are often tasked with the responsibility to observe and report criminal activities, and if they personally observe a crime being committed, they are within their rights to detain the suspect to prevent further illegal activity and to protect themselves and others.

This action should always be done in a lawful manner and in line with the policies and procedures of their employment, ensuring the safety of all parties involved. The justification stems from the need to maintain order and security, fulfilling the guard's role in protecting property and people.

Other scenarios, such as someone behaving unusually, being asked by a friend, or feeling threatened, do not provide sufficient or lawful grounds for a detention. These situations might warrant a different response, such as monitoring the individual or contacting law enforcement, but they do not align with the legal standard necessary for detaining someone. Thus, witnessing a crime stands out as the clear and appropriate basis for a security guard to take such action.