I used to play tennis,
but not anymore
A pen pal of darkness,
though you hate our speech
A friend of a friend
of a bar and a horse
In children's games,
I help with the layout for each
I am down to Earth
I wouldn't be a great dam,
But for what it's worth
Can you guess what I am?
I think you are
Chalk
I used to play tennis,
but not anymore
Chalk used to be used to mark Tennis Courts, now I believe paint is far more common.
A pen pal of darkness,
though you hate our speech
Used to write on blackboards, sometimes squeaking most unpleasantly
A friend of a friend
of a bar and a horse
Used on hands in Gymnastics, including several events involving Bars, and the Pommel Horse
In children's games,
I help with the layout for each
Chalk used to mark lines for a bunch of kid's games, including Hopscotch and FourSquare
I am down to Earth
I wouldn't be a great dam,
Mineral from rock or soil, but dissolves in water.