What is the name for their weapon that is made from 3 hard rock leather balls tied to a rope?

The weapon you are referring to is commonly known as a "three-section staff" or "three-section nunchaku." However, if you're specifically mentioning a weapon consisting of three hard rock leather balls tied to a rope, it might resemble a "three-ball flail" or "morning star," depending on its design and usage. These weapons are designed for striking and can be quite effective in skilled hands.