Which rope is used by a Tie Down roper to secure the calf's legs?

The Piggin String is the correct choice because it is specifically designed for the purpose of tying the legs of a calf during tie-down roping events. This lightweight, durable rope allows the roper to quickly and effectively secure the calf after it has been caught.

In rodeo competitions, efficiency and speed are critical, and the piggin string is crafted to ensure that the roping process is as swift as possible. This type of rope is made from materials that provide the right balance of strength and flexibility, allowing for a secure knot that holds the calf's legs together without risk of injury.

Other ropes, such as ranch ropes and wool ropes, serve different functions in the rodeo and ranching context. Ranch ropes are generally used for general cattle handling, while wool ropes are less common in competitive events and often lack the specific qualities needed for tie-down roping. The calf rope, while it may initially seem plausible, is typically used for the act of catching the calf rather than securing it afterward. Thus, the piggin string is the ideal tool for this task.