I'd say it's an SD for negative reinforcement.

You're thinking it's an EO for running, but if you get more specific and say "running from zombies," the EO isn't really changing. By that, I mean, the reinforcement (escaping a terrible death) is probably always pretty high. But it only occurs when zombies are nearby (SD).

So the zombies chasing you is an SD that running away will provide reinforcement.

Similarly, if you were hungry (increases reinforcing value of food; high MO for food) but you can see there is no food in the kitchen, you're not going to engage in behaviors that typically acquire you food. Food is still much more reinforcing, but there is no indication of food-acquiring behaviors being reinforced (SD).