Essentially, I agree the ball "moved," but returned to its original position. However, I do think Clark should have been penalized for improving his lie by clearly pushing down on his club behind the ball, rather than lightly "grounding" his club. Really, isn't the question whether it was even possible to "lightly ground his club" in the deep rough without improving his lie? As such, wouldn't it be on the player to not ground his club at all in order to avoid a penalty? Does this situation create a conflict between the rule permitting the lightly grounding of one's club behind the ball and the rule prohibiting one from improving their lie?