We did that once, in my friends front yard. We hit my elementary school music teachers car, in broad daylight. She pulled into the driveway and knocked on the door, his mom answered, and yelled at him. Cops ended up at my friends house.
When I was visiting a friend in California, we were throwing oranges and water balloons at cars. The house was on a corner of a small road and a 4 lane highway, with railroad tracks running through the back yard. When the train gate went down, cars would back up and we would throw balloons at cars. Some people got out and yellled at us. Someone threw one at a guy pushing a stroller. It bounced off him and landed in the the stroller, but didn't pop. He picked it up and looked around confused.
Later, we threw them off the roof of an RV at cars on the 4 lane road, and one right down on a car at the stopsign in front of the house. The guy got out and yelled at my friends, asking "Who Throw water balloon at my car!?"
It was silly, then a cop came.
He didn't really do anything, though. He told us we should stay inside because it was hot, we had AC and a big TV with an xbox