Which of the following commands would indicate a police officer is actively needing assistance?

The command indicating a police officer is actively needing assistance is the request for backup. This phrase is universally understood in law enforcement communication to signify that an officer is facing a situation that requires additional support, typically because they are possibly in a dangerous or high-stress scenario. The urgency of this request prompts immediate action from other officers in the vicinity, emphasizing the need for assistance without any ambiguity.

In contrast, commands like "on patrol," "requesting case number," and "in the field" do not communicate an immediate need for help. "On patrol" simply indicates that an officer is conducting routine duties; "requesting case number" pertains to administrative tasks and does not imply any urgency; and "in the field" is a broad term that means an officer is out of the station but does not imply any need for backup or assistance. Thus, the request for backup clearly stands out as the urgent call for aid that defines the officer’s immediate situation.