I first saw this drill in a Carolina PGA Teaching Seminar given by PGA Professional, Mike Malaska. I immediately enjoyed his instructional speach and could see the benefit of using a Tennis Racket to explain the term square. I truly feel that a simple drill like this can teach you how to stay more square and also create more wrist lag as you transition into the down swing. Start by going smooth and slow and work into a slightly quicker motion. Go as slow as you can to feel your positions. I use this drill a lot at home, when I can't hit balls. Give it a try, or call me for a lesson at Wildwood Green Golf Club. I'd be happy and honored to help you through the racket / swing guide drill.