The yard on the first floor is not allowed. What about throwing things upstairs?

The most direct way is to complain to the property.

If the complaint doesn't work, in order to protect yourself, you have to stop going to the outdoor activities of 1 floor frequently to avoid being hit by high-altitude parabolic objects.

Next, if the upstairs continues to throw things downstairs after the property is involved in the disposal, then you have every right to call the police at this time. I think when the police come, most people will be afraid and won't throw anything downstairs again.