We had a huge hill in our elementary schoolyard. There was a "hiking back up the hill" section to reduce collisions of sledders going down and those going back up. Right before the end of recess we always tried to sled down the up-hill against the grain of traffic, but you had to make it look like you didn't try to. We called it bowling. Induced some major casualties and got ourselves in trouble a few times.My elementary school had a couple inner tube runs that produced at least 1 casualty a week!