This decision is an easy read. It's short enough that you might want to skip my summary and just read the decision.
Uniformed officers investigating narcotic transactions converged on an area where they expected to find drug dealers, a large crowd of customers, and lookouts (so it was a nice neighborhood). Wardlow was sitting outside of a building nearby holding an opaque bag, and when he saw the officers he suddenly took off running. The last car in the officers' caravan followed him, caught up to him shortly afterwards, and the officers detained him for further investigation. Because illegal drugs and weapons go hand in hand, one of the officers searched Wardlow for weapons. He found a loaded gun, and Wardlow was eventually convicted of being a felon in possession of a firearm.
Wardlow appealed, arguing that the police had no reason to stop him. The argument goes that simply being in a high crime area is not a reason to stop someone, and that Wardlow's sudden, unprovoked, headlong flight from officers was essentially his way of exercising his right to go about his business and decline to speak to officers who he was under no obligation to speak to. And the Chicago Supreme Court agreed with him.
This appeal made its way to the US Supreme Court, which held that Wardlow's detention was valid. The court recognized that simply being in a high crime area does not constitute reasonable suspicion, and neither does declining to speak with the police. But being in a high-crime area (particularly under these circumstances, where the officers arrived in force because they expected a lot of crime to be going on right now) is a factor in building reasonable suspicion. So is nervous, evasive behavior -and headlong flight is sort of the O.G. of nervous, evasive behavior. Running away isn't "going about your business," it's the exact opposite: it's dropping whatever you're doing in an attempt to get away from the police.
Still, none of this is criminal. It's not a crime to be present in a bad neighborhood, and it's not a crime to run away from the police. There are perfectly legitimate explanations for these things. But the Fourth Amendment accepts that the police will sometimes stop or even arrest innocent people. A stop only needs to be justified by reasonable suspicion, not by actual guilt. If additional information isn't discovered to justify arresting the suspect or prolonging the stop, then the suspect has to be released, but in this case the officers found a reason to arrest Wardlow right after they stopped him. His conviction was upheld.