It depends on what you do with YOUR shoulders and swing. While strictly one or the other is not possible, you can favor one or the other depending on the amount your upper body is tilted forward. When the hips move leftward the right shoulder drops: that is "perpendicular to the ground." When you rotate like a baseball batter, that is perpendicular to the spine.
Both motions occur in sequence in the best swings in various degrees, the hip slide to the left initiating the first, followed by "slamming the door" into and after impact.
Which is called a compound pivot by some; other names by others.
