Under what circumstances can a security guard physically detain someone?

A security guard can physically detain someone when there is reasonable belief that a crime is being committed. This principle is rooted in the legal concept of "citizen's arrest," which allows individuals to detain another person under specific circumstances. In this case, the guard must have a reasonable belief based on observable facts that a crime is taking place or has just occurred, allowing them to act within the bounds of the law to prevent further criminal activity or to preserve evidence for law enforcement.

The other options do not provide a legitimate basis for detention. The request of any customer does not equate to legal grounds for detaining a person, as it lacks the necessary foundation of witnessing a crime. Similarly, detaining someone simply for being rude does not constitute a crime and thus does not meet the criteria needed for reasonable detention. Lastly, feeling unsafe is subjective and does not provide sufficient justification for physical intervention unless it is clearly linked to a recognized threat or criminal activity.