"Hemelrijken10a" by Robert de Greef (bewerkt door Lempkesfabriek) -  van Robert de Greef. Licensed under CC-BY-SA-3.0-nl via Wikimedia Commons.
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.