Supine leg slides with a ball in crook ("Hamstring curl on ball" Core/abdominal stabilization, with pelvic tilt - single leg)

Lie on your back with your knees bent and one foot balanced on a medium sized ball.
Flatten your lower back against the floor and tighten your abdominal muscles.
Roll the ball away from you by straightening your leg.
Do not allow the ball to roll side to side.
Roll the ball back towards you by bending your hip and knee.
This movement should be slow and controlled.