Wiktionary
nerf ball
n. Any small foam ball, soft and very light, designed for indoor use.
Usage examples of "nerf ball".
The triplets were having a game of monkey-in-the-middle with a small orange Nerf ball.
He was sitting on the floor of the corridor, tossing the Nerf ball back and forth to Sheena.
They suggested that the planet was his Nerf ball, a toy that he could squeeze, or rend, or bounce madly around with impunity.