Any ball which strikes the crossbar and moves down and forward will have backspin. The question is how far forward it will move. You appear to believe (and correct me if I am wrong) that the ball would have to move forward far enough to cross the line, based on the fact that it struck the crossbar again when it came back up. As I mentioned in my last post, I was involved in a game where it did not cross the line and struck the crossbar a second time. All I can tell you that it is possible, what you claim we should assume cannot happen, I have seen happen. I believe you mean "physics." Though odds are a psychic would have just as good a chance at determining if the ball crossed the line as the AR.