Ryan Young demonstrates Under the Leg (UTL) sets, also called Leg Over set. Once you have gained control over the center delay, this is the next step in improving control and in beginning to do tricks with the center delay. UTL sets are probably the most used restricted set in freestyle frisbee.
Start with a center delay. Bring the disc low while keeping your upper body upright. Then left one leg and move it over the disc. Now, set the disc into the air by lifting the delay hand quickly. Put your leg back down and regain the disc on a nail delay.
Ryan also shows us all possible combinations of hands and legs. A great challenge for new players is to try to learn each one. And then ask yourself, is this really all of them? How else might I restrict my movement to gain more control over the frisbee? If you come up with another option, let me know if the comments.