This is an awesome DIY tetherball pole we got at an estate sale and bought a new ball and rope for.
But it was really cleverly made.
The base is a tire with a circle of plywood underneath and a short length of pole (about two feet) inserted in the middle and concrete poured around.
The second piece is the outer pole, which sets on top of the little one. On the top is a round hook which you carebeaner (or tie) the ball onto.
Great find (and you could really DIY one like it).