A Cleveland detective watched three men repeatedly casing a storefront, stopped and frisked them, and found a concealed weapon. The Court held that a brief investigative stop and pat-down for weapons — later called a 'Terry stop' — is permissible on 'reasonable suspicion,' a lower standard than the probable cause needed for arrest. Terry stops are the doctrinal basis for stop-and-frisk policing and one of the most consequential (and contested) balances the Court has struck between officer safety and Fourth Amendment liberty.