Stand in good body alignment (abs tight, chest up, back straight) with feet in comfortable position. Hold medicine ball in front of body and keep feet flat on floor throughout entire exercise. In a controlled motion, rotate the body to one side and toss ball to partner or against wall. Once you catch the ball on return, rotate the opposite direction and repeat toss. While maintaining the controlled motion, continue rotating left and right to desired number of repetitions. Do not allow muscles to relax before next repetition.
Here are a few suggested alternative exercises:Ab Crunch ObliquesBall Crunch TraditionalDumbbell Side BendsLateral Bend with Barbell