The specific case before them involved an anonymous woman who called 911 to report a driver who forced her off the road. She gave the driver's license plate number and the make and model of his car as well as the location of the incident in question. Police officers later found him, pulled him over, smelled marijuana, and searched his car. They found 30 pounds of weed and subsequently arrested the driver. The driver later challenged the constitutionality of the arrest, claiming that a tip from an anonymous source was unreliable and therefore failed to meet the criteria of reasonable suspicion, which would have justified the stop and search. Five of the nine justices disagreed with him." The ruling itself (PDF).