What must a lawful "stop" be based on?

A lawful "stop" must be based on reasonable suspicion of unlawful activity. This means that an officer needs specific and articulable facts that lead them to believe that a person may be involved in criminal activity, rather than just a hunch or random suspicion. The concept of reasonable suspicion originates from the need to balance individual rights against the need for law enforcement to maintain public safety. It allows officers to take appropriate action when they observe behavior that raises a suspicion of unlawful conduct. This standard is lower than probable cause, which is required for making an arrest, emphasizing that stops can occur based on less definitive evidence than what would be needed for an arrest. Thus, the rationale behind reasonable suspicion is to provide officers with the ability to act on observed behaviors that could pose a threat or indicate that a crime is being committed, while still respecting individuals' rights against arbitrary or invasive actions.