Whether an officer's street encounter, forcible stop, and patdown for weapons are governed by the Fourth Amendment even though they do not amount to a formal arrest or a full evidentiary search.
Holding
Yes. A forcible stop is a seizure, and a patdown of a person's outer clothing for weapons is a search; both must be reasonable under the Fourth Amendment.
Reasoning
The Fourth Amendment protects personal security on public streets as well as privacy in homes and other private places. The Court rejected the suggestion that a stop and frisk falls outside the Amendment merely because it is less intrusive than a formal arrest and a full search.
When Officer McFadden grabbed Terry and restricted his freedom to leave, he seized him. When the officer explored the outer surfaces of Terry's clothing to find weapons, he searched him. A public patdown is a serious invasion of personal security, not a trivial inconvenience.
The governing inquiry is therefore reasonableness in all the circumstances. The Court framed that inquiry in two parts: whether the officer's action was justified at its inception, and whether the action was reasonably related in scope to the circumstances that initially justified it.