Terry stops are for the purpose to investigate. If an officer has “reasonable suspicion” that a crime has been committed or is about to be committed, that officer can seize the person to conduct an investigation to confirm or dispel the officer’s suspicions. You can think of it as freezing everything, maintaining the status quo, for the officer to determine what is going on.
Legal Supplement
Terry v. Ohio, 392 U.S. 1 (1968),
It must be recognized that whenever a police officer accosts an individual and restrains his freedom to walk away, he has seized that person.
Cupp v. Murphy, 412 U.S. 291 (1973),
[D]etention of the respondent against his will constituted a seizure of his person, and the Fourth Amendment guarantee of freedom from unreasonable searches and seizures is clearly implicated.
U.S. v. Mendenhall, 446 U.S. 544 (1980),
We conclude that a person has been seized withing the meaning of the Fourth Amendment only if, in view of all the circumstances surrounding the incident, a reasonable person would have believed that he was not free to leave.
Michigan v. Chesternut, 486 U.S. 567 (1988),
While the very presence of a police car driving parallel to a running pedestrian could be somewhat intimidating, this kind of police presence dies not , standing alone, constitute a seizure.
Berkemer v. McCarty, 468 U.S. 420 (1984),
[T]he officer may asked the detainee a moderate number of questions to determine his identity and try to obtain information confirming or dispelling the officer’s suspicions. But the detainee is not obligated to respond.
U.S. v. Place, 462 U.S. 696 (1983),
[T]he Court acknowledge(s) the authority of the police to make a forcible stop of a person when the officer has reasonable, articulable suspicion that the person has been, is, or is about to be engaged in criminal activity.
Reid v. Georgia, 448 U.S. 438 (1980),
[A]ny curtailment of a person’s liberty by the police must be supported by at least a reasonable and articulable suspicion that seized person is engaged in criminal activity.
Texas v. Brown, 443 U.S. 47 (1979),
[E]ven assuming that the purpose [to prevent crime] is served to some degree by stopping and demanding identification from an individual without any specific basis for believing he is involved in criminal activity, the guarantees of the Fourth Amendment do not allow it.
