A skill-based nongame.
It´s hard to keep the balls in the air, and although you can count the number of times you do that to set yourself a goal, I think the fun of the game is more in the state of flow one can achieve when juggling. It´s also a test of resistance and focus.
Also a great metaphor for times you´re too busy with many things at once.
Verbs: throw ball, catch ball
Nouns: Balls (3 to 4 - Pros can handle even more)