John Marshall Harlan II

“ In the first place, if the frisk is justified in order to protect the officer during an encounter with a citizen, the officer must first have constitutional grounds to insist on an encounter, to make a forcible stop. Any person, including a policeman, is at liberty to avoid a person he considers dangerous. If and when a policeman has a right instead to disarm such a person for his own protection, he must first have a right not to avoid him but to be in his presence. ”

“ Where such a stop is reasonable, however, the right to frisk must be immediate and automatic if the reason for the stop is, as here, an articulable suspicion of a crime of violence. Just as a full search incident to a lawful arrest requires no additional justification, a limited frisk incident to a lawful stop must often be rapid and routine. There is no reason why an officer, rightfully but forcibly confronting a person suspected of a serious crime, should have to ask one question and take the risk that the answer might be a bullet. ”

“ Officer McFadden's right to interrupt Terry's freedom of movement and invade his privacy arose only because circumstances warranted forcing an encounter with Terry in an effort to prevent or investigate a crime. Once that forced encounter was justified, however, the officer's right to take suitable measures for his own safely followed automatically. ”