The rules of soccer on a tennis court are simple. At least, I'm guessing they are. I went out for a late-evening quick, limb-loosening stroll-wth-occasional-jogging tonight, and while circling Brooklyn School Park about a block north from my apartment, I looked at, really looked at, the people on the tennis court at the park's northeast corner. They were kicking and heading a soccer ball back and forth over the net. There were eight people, four on a side, and they were keeping points -- I heard one of them say "13 to 16" -- so there were probably rules. (Hey, even Calvinball has rules.)
That was controlled kicking and heading of that soccer ball, by the way. Tennis courts are small. No MLS action here, because that action's taking place on a 110-by-70-yard (or 120-by-80-yard) rectangle and thus requires lots of running and hustling. But the very idea of taking a soccer ball to a tennis court MUST BE SHARED.