The leash is designed to be attached under the knee, and not to the ankle.
Attaching the leash under the knee prevents it from dragging in the water or under your feet, and allows for greater leg power in the event of a fall, in order to hold the board, which is large and heavy.
In the case of great impact, the leash can break to avoid hurting the user. Not suitable for surfing in large waves (Over 0,5 m).