In what circumstances will the police have reasonable cause to detain a man in a parking lot?

In People v. Aldridge, supra, 35 Cal.3d 473, 198 Cal.Rptr. 538, 674 P.2d 240, the defendant, who stood in a group of people gathered in a liquor store's parking lot, ran when a police car entered the lot at 10:15 p.m. This conduct by the defendant, coupled with the fact that the parking lot was a place where drug activities were common and people were frequently armed, prompted the officers to stop the defendant for questioning. One of the officers had made over two hundred arrests in the area and knew that a few hours earlier other officers had made three narcotics arrests in the parking lot. Based on this evidence, the trial court ruled that the police had reasonable cause to detain the defendant. This court disagreed.