Picnic tables, along with any other park or course equipment, are obstacles on the course. They are to be treated as any other obstacles, for example a bush or a tree. How you play your next throw depends on the picnic table. If there is room for you to take a stance under it, even by sticking your leg underneath, that’s what you do. If your disc is on top of the picnic table and there is room underneath, it is a lie above ground, and you mark directly below it and play from there. If the disc is on top and there’s no room underneath, the table is treated as a solid obstacle, and you mark directly behind it on the line of play.