Not reliably. From a single photo, apparent subject size depends not just on real height, but also on perspective — and perspective is determined by camera position. To estimate how far back another runner is, you need at least one key missing piece of information, such as:

• the camera-to-subject distance for one runner, or
• the lens focal length / field of view

Without that, there isn’t enough information to solve the problem. Different lenses can make subjects at different distances look deceptively similar in size: telephoto lenses tend to make depth look compressed, while wide-angle lenses exaggerate spacing. So even if you assume each runner is about 1.8 m tall, the photo alone does not let you accurately recover the distance between them.

In short: with no lens data, no camera distance, and only one image, you can’t make a dependable distance estimate.