Kei Nishikori sets up his two-handed backhand in textbook fashion, and his body coils with the shoulders turned to the net in excess of 90 degrees. This allows him to hit with surprising power and plenty of spin.
The secret to Nishikori’s two-hander is understanding the backward rotation of his arms and racquet at the bottom of his backswing. His left arm rotates so far backward that the underside of his forearm is turned partially to the sky. Because of this, the tip of his racquet is tilted downward toward the court.
As the forward swing begins, Nishikori’s arms and racquet rotate radically upward in the opposite direction, significantly increasing the amount of upward lift—or brushing effect—when the strings contact the ball. This is the backhand equivalent of the windshield-wiper forehand finish.
The downward tilt of the racquet head allows Nishikori to generate additional acceleration at the moment of contact. Extra spin—Nishikori can rotate the ball in excess of 2,000 r.p.m.—is also a result of his backward rotation. Experiment with the windshield-wiper finish yourself to increase your velocity and topspin.