A "Bachelor's degree in Law" exists in the UK and many other countries, where it allows you to become a lawyer.
But the U.S. is an exception. In the U.S., to become a lawyer requires a "Juris Doctor" degree, which is a 3-year course of study that you start after obtaining a Bachelor's degree.
Some students, knowing they intend to be lawyers, get their undergraduate (Bachelor's) degree in a major called "Pre-Law". Others may get a Bachelor's degree in a different major. It depends on what is required by the school where they plan to enter the Juris Doctor program.