When police make a traffic stop, a passenger in the car, like the driver, is seized for Fourth Amendment purposes and so may challenge the constitutionality of the stop. A police officer observed a vehicle displaying a permit that allowed it to be driven legally even thought the registration tags were expired. Although the officer admitted that there was nothing unusual about the permit or the way it was affixed, he nevertheless decided to pull the car over to verify that the permit matched the car. Upon stopping the car, the officer recognized passenger Brendlin and ran a warrant check on him and after verifying that he was a parole violator arrested him. A search incident to arrest revealed methamphetamine and related items. The Court held that Brendlin was seized from the moment the car came to a halt as a reasonable person would not have felt free to leave. Because the seizure was unlawful, being without cause, it was error to deny his suppression motion on the ground that the seizure had occurred only at his formal arrest.