Which of the following is NOT a legal catch in team roping?

In team roping, the legal catches are well-defined to ensure fairness and safety during competitions. A catch is considered legal if it meets specific criteria depending on the part of the animal that is caught.

Catching the back legs is not recognized as a legal catch in team roping. The rules dictate that only certain areas of the steer or calf can be caught for the roping to be considered valid. Legal catches include half of the head, where the loop encompasses one side of the animal's head, the whole head, which allows the rope to go all the way around, and catching both horns. Each of these catch methods allows for both the horse and the roper to control the steer effectively, leading to a successful completion of the roping task.

In contrast, catching the back legs does not align with the competitive standards of team roping, as it can cause undue stress on the animal and does not facilitate an effective stop or control of the steer. Therefore, the identification of catching the back legs as the option that is not a legal catch accurately reflects the established rules in the sport.