A Runner is a practitioner of parkour.
Terrestrial & air vehicles are heavily tracked and surveilled, and subject to VehicleCommandeering. Conventional foot traffic is subject to bottlenecks, surveillance, and invasive checkpoints. Mass transit is practically tailor-made for an invasive state or corporation to know what you're transporting.
Effectively, parkour is often one of the only ways to get somewhere in a sprawl unmolested. This is useful for spies, couriers, and anyone else who needs to travel quickly and discreetly.