Stand with the heel of the involved leg raised (can use yoga mat or something similar). The uninvolved leg is moved back to provide balance. As you hinge forward, keep hips square; for example, if the right leg is in front, actively pull the right hip back and left hip forward. Ensure that the back is kept straight as you bend to pick up the medicine ball. If you can't keep back/legs straight, elevate the ball onto a table or chair. Focus on keeping weight in heel and coming up out of hinge by activating front glute/hamstring and NOT back arching low back and pulling up from shoulders.