Tetherball Poles, Sets, Balls, and Courts
A tetherball is much like a volleyball, except that it needs some way to be attached to a rope. The attachment comes in two types: a loop protruding from the tetherball's surface or a bar recessed below the surface. I recommend the second type. The protruding loops tend to break faster, and when they get hit, they hurt the player's hand. The recessed bar is a little harder to get the rope through when you first set up your court, but it's well worth that extra bit of effort, as hitting the reinforced part of the tetherball near the bar hurts much less than hitting the loop, and it's nearly impossible to hit the bar itself.
Tetherballs vary quite a lot in how soft they feel when hit. Most tetherballs are made much too hard; your hands can start hurting pretty quickly, and an accidental hit on the wrist has quite a sting. The "Super Soft" type is most comfortable, and you don't give up any other qualities to gain that comfort.
Recommended Tetherball Poles and Tetherball Sets
Even though the tetherball doesn't weigh very much, it exerts fairly strong forces upon the pole. The thin, lightweight sectional poles that come in some tetherball sets are not up to the task. They wobble so badly, they ruin the ball's flight path, and eventually they bend or break. One-piece tetherball poles are by far the sturdiest, but they're also expensive, primarily because of the shipping. Next best are heavy-duty poles that come in two sections and have at least a 2" outer diameter; they're not quite as indestructible as a solid pole, but they will stand up to normal use, and they're a lot less expensive to ship. If you're comparing sectional poles, more weight at a given diameter is better, as it indicates thicker steel.
Building a Tetherball Court
A full-sized tetherball pole 12' long should sit 2' deep in the ground so that it rises 10' above ground level. Dig a hole 2.5' deep, with a 2' diameter, pour a 6" concrete footer, let it set, then set a 2' sleeve (a piece of larger pipe) in the hole with something to keep it in place while the surrounding concrete sets. The sleeve should provide a fairly tight fit for the tetherball pole it will hold, and it should protrude just enough above ground level to keep soil from falling in, yet not high enough to be hit by a lawn mower, if relevant. When the pole is removed, a small cap to keep debris out is a good idea. Make sure the sleeve sets up perfectly plumb.
Although the most common site for a tetherball court is on a lawn, heavy use will turn that area into mud in short order. Extra driveway space can make a great site, as can a gravel area, both of which make it easier to play while the ground is still wet after a rain. Falling should be very rare for most players, so a hard surface should be safe.
No outer boundary circle is needed for the court, because there's no advantage to getting very far from the pole, but it's best to have at least 8', preferably 10', of clear, level ground all around the pole. The only boundary needed is a line dividing the court into two equal halves.
One setup that is definitely unsafe is using some kind of a portable stand as a base. While tetherball players rarely fall, they constantly jump, and coming down on the edge of the stand will almost certainly cause an injury. I have seen portable stands used in supervised indoor paddle tetherball, but intense vigilance is required by the supervisor, and this choice is not recommended.
The rope's length should be set so that the bottom of the ball ends up two feet above the ground when the rope is not wrapped and the ball is at rest.
Paddle tetherball is best reserved for players with enough self-control to avoid swinging a paddle or racquet where it might hit an opponent and likely cause significant injury. Even a collision between paddles or racquets can be dangerous. Paddle tetherball probably evolved in response to the discomfort of hitting hard tetherballs with bare hands. With the current availability of much softer tetherballs, paddle tetherball may no longer be a sensible choice.
Commercially made pole, ball, and paddle sets do exist, but usually people just use old tennis balls with a rope poked through at about 10:00 and 2:00. The best way to make the holes in the tennis ball is with a power drill and a 1/2" bit. Hold the ball in a clamp while you drill. The bit can slip off the ball easily, so you don't want your hand in the way.
The only difference in the pole requirements for paddle tetherball is that a lighter pole might do, because the ball is so much lighter. A portable base is still unsafe. Set the lighter pole in the ground if at all possible.
Paddle tennis racquets make good paddle tetherball racquets, and Jokari paddles or aluminum junior tennis racquets will do. Racquetball racquets work well, but they'll wear out quickly hitting the heavier ball and, occasionally, the pole. A wrist string should be worn with any kind of paddle or racquet to keep it from flying out of the hand and hitting someone.
In paddle tetherball, the ball flies fast and sometimes unpredictably. It's also small enough to injure an eye. Wear eye protection. The type used for racquetball will work perfectly.