I had a question come up today. It was a clinic, four and a pro. We were playing out points, and there were balls on the court near the curtains. There was also a lesson going on next door, with balls sprayed onto our court from time to time. In the middle of a point, I saw a ball rolling around on our court behind my two opponents. I called a let immediately so no one would get hurt. The pro said my let call was incorrect. He said that since the ball had been there all along, no player could call a let for that ball. My let call was wrong, so we should lose the point, he thought. Now, this was clinic and so was a bit unrealistic because none of us plays matches with 20 balls along the side and back curtains. Further complicating matters is that I had no idea what caused that ball to start moving. I don't think my opponent struck the curtain to move it or kicked it, so it is possible it rolled over from the adjacent court (or it was along our side curtain and player on adjacent court caused it to roll). I was kind of puzzled by this. I thought my opponents could not call a let for a ball they allowed to sit on their court (or a ball that fell out of their pocket). But I thought I could always call a let for a ball rolling onto my opponents' court regardless of where the ball came from. Here's the only thing I could find in the Code, which doesn't really address this situation.