The pop-up usually results from having no spine tilt at address, or the left shoulder is lower than the right. It's also caused by incorrect sequencing on the downswing. Above, I've tried to mimic that action: With no spine tilt I began the downswing by leading with my chest and arms, not my hips.
First, the easy fix: Tilt your spine away from the target at address, setting your head behind the ball (above, inset). To ingrain the feeling at impact, hold a shaft or alignment rod on your chest and get in the impact position (right). Practice turning so the rod points several inches in front of the ball at impact. The sequence: hips, chest, arms, hands, club.
*Matt Killen, one of Golf Digest's Top-20 Teachers Under 40,
is based at The Club at Olde Stone in Bowling Green, Ky. He works with Kenny Perry, J.B. Holmes and a number of other tour players. Read more about Matt Killen.