Shabbat, Chapter Eleven, Mishnah Three
It is forbidden to carry something four cubits in the public domain. Our mishnah deals with someone who throws something four cubits in the public domain and some nuances concerning this halakhah.
1) One who throws [something] four cubits on to a wall:
i) if [the wall] is above ten handbreadths, it is as if he throws it into the air;
ii) if below, it is as if it he throws it on to the ground.
(a) And one who throws [something] four cubits on the ground is liable.
2) If one threw [something] within four cubits and it rolled beyond four cubits, he is exempt;
a) [If one threw something] beyond four cubits and it rolled within four cubits, he is liable.
Section one: According to the rabbis, above ten handbreadths is no longer the public domain, but neither is it a private domain. It is called a makom patur, a place that is exempt from the laws of carrying. Therefore, one who throws something onto a wall that is higher than ten handbreadths is exempt. However, if she throws it and it goes four cubits and lands on a wall lower than ten cubits, it is as if the object landed on the ground and she is liable. This is because someone who throws something four cubits on the ground is liable.
Section two: This section deals with throwing something that afterwards rolls. If she throws the object less than four cubits and it rolls further, she is exempt. This is because she did not intend to throw something four cubits. Alternatively, she is exempt because the object didnt at first land the necessary four cubits away. However, if she threw something four cubits and then it rolled back she is still liable because it did land four cubits from where she threw it.