How do you you say tetherball in Swedish?

I don't think there is a word for it so you can either use tetherball or make a new word. Tether = Tjuder (from Tjudra) so Tjuderboll would be a literal translation, it doesn't really sound nice though and noone will have a clue what you're talking about so I'd suggest you use Tetherball and then explain the game.