Important Roles of Non-Dominant Hand in Forehand Groundstrokes
Andre Agassi
Look what these players are doing with their non-dominant hand. Some put their opposite hand (non-dominant) on the racket;some put it on the throat of the racket. The most importance thing about utilizing racket back is to have a good shoulder rotation.
Maria Sharapova
Sam Stosur
Andy Roddick
James Blake
Tennis forehand - modern forehand review
"power" forehand inside out - highspeed study
Novak Djokovic - Slow Motion Forehands, Australian Open 2012