Terry v. Ohio

A police officer can stop and pat you down if they have a specific, articulable reason to suspect you of criminal activity — not just a hunch. They don't need a warrant or full probable cause for a brief investigatory stop.

Police may briefly stop and frisk a person based on reasonable articulable suspicion of criminal activity, even without probable cause for arrest.

Established the "Terry stop" — the legal basis for nearly every police stop. If an officer stops you, they need reasonable suspicion, not just a feeling.