It's been illegal for a few years now, but I hardly ever see it called. Actually, Clark got away with it twice in that period before it was called the third time. I was screaming at the television and explaining to my wife that he was getting away with an illegal move. I'm not sure where the line is though. I think you are allowed to do it as long as you have at least one of your feet on the mat. They just want to stop people from jumping and cutting back over both at the same time. It seems weird that it is illegal still though because it isn't going against a joint. All you are doing is forcing the knees to bend the way they are designed to bend.