The video here shows Mabel the robot running. When you run you’re feet actually leave the ground and as you can see in this video, so do Mabel’s feet. I can’t imagine this is easy to accomplish in a robot.
Mabel is a collaboration between Jessy W Grizzle at the University of Michigan and the Robotics Institute at Carnegie Mellon. Mabel can run at a top speed of 6.8 miles an hour.