The bleachers in our gym used to pushed up flat against the wall in high school so we could play ball in P.E. class and every once in a while an errant pass or tip would cause a ball to land on the top and get stuck in the bleachers. Anyways, I climbed up to get it one day and had the genius idea to jump off the top bleacher and upon impacting the ground, dribble it between my legs. The rest, as indicated by my quoting of your post, is self explanatory.
The one highschool gym I played Basketball at had a warped key. Though I've never been injured myself doing this, I've seen players taking an weird bounce and sacking them square in the nuts.