Mark is another example of a great looking swing at regular speed with nice plane lines and fluid, rhythmical motion, but one that exhibits room for improvement in the impact area. It’s not easy to get a clear sense of a player’s grip in an online situation but here it’s obvious that Marks grip is on the weak side, and with a bit of extra forearm rotation in the first part of the backswing his clubface gets extremely open. This lasts all through the swing so that when the club is approaching impact it is still so open that Mark has no choice but to allow himself plenty of time to twist the face closed to square it at impact, which would be a good reason to see what we have here as the hands approach from a wide position and appear to flip into impact. If Mark didn’t use this procedure and tried to delay the clubhead and get his hands more in front of the ball to compress it better, he would simply hit every shot dead right. The need to allow time to close the face may also be encouraging Mark to sway back with his hips in the backswing and then not move laterally enough to get pressure onto the left leg at impact. My suggestions here start with strengthening the grip, after which Mark needs to focus on keeping his hips in the face on box in the backswing. If the grip change does not close the face enough Mark can try to eliminate some of the forearm rotation in the backswing that helps roll the face open, and might also try flattening the left wrist at the top of the swing.