The following excerpt from the International Sky Grace Rhythmic Gymnastics Clubs Association rules is dedicated to the leg-on-shoulder balance.
13. Leg on shoulder, with or without hands
The split required. The foot or calf is placed on the shoulder with or without the help of hands (the leg is held with the help of the chin).
It can be performed in two versions - with and without the help of hands. However, the cost of the element varies.
Let's look at two examples: in the first instance, the gymnast in the video will receive 0.40 points, since she is holding her leg with her hands, and in the second case, it's done without using her hands, she will receive 0.50 points.
The full version of the International Sky Grace Rhythmic Gymnastics Clubs Association rules is available here:
International Sky Grace Rhythmic Gymnastics Clubs Association rules.