In New York City they were part of children's social game drawn on
asphalt with chalk. A square usually, with small diagaonal corners or
1/4 circles, with a small square in the middle of the larger square
divided diagonally into four. At opposite corners numbers were
ordinally marked in chalk. The idea was to go from each of the
numbers, one to the next in series flicking the upside down crown cap
completing the series by landing in the area demarcated by the drawn
perhaps all triangular within the two nested squares. I think some
were qweighted with wax or gum, etc., the painted surface of the crown
cap sliding over the concrete or asphalt. I heard it called as a kid
as "Bottlecaps" in the South Bronx, NY or Skelly.

(Skelly (or skelsy, skellzies, scully, tops, caps)

http://www.barrypopik.com/article/810/skelly-or-skelsy-skellzies-scully-tops-caps