Spring rider

A Dutch spring rider.

A spring rider or spring rocker is a bouncy, outdoors playing device consisting of a metal spring beneath a plastic or wooden central beam or flange, with 1 to 4 plastic or fiberglass seats above it. When a person sits on it, the structure moves and bounces. Spring riders are common in many playgrounds.^[1][2]

References

Wikimedia Commons has media related to Playground springs.