Take position hanging from the pull-up bar with a medium or narrow, underhand or neutral grip, whatever feels more comfortable. Let your body hang down freely. This is the starting position.
Commence the movement by contracting your abdominals and taking the outstretched legs through a clockwise rotation from the starting position right back around to the same position. Your legs are outstretched with a slight knee bend and the rotation comes from the hip.
When back at the starting position after a clockwise rotation, reverse the movement and perform the same manoeuvre in an anti-clockwise direction.