A club is called “across the line” if it is too steep in the swing’s upper half. By the upper half, I mean the part after the club has traveled more than 90 degrees in the backswing and has not yet reached the same point in the downswing. Across the line without any qualifier means the club is too steep at the top of the backswing. If it steepens right after that, it is called “across the line at transition.” Sometimes the club may become too steep not until the downswing is well on its way. But one would only call this case across the line if the club still flattens in the second half of the downswing.