—In addition to the link in my comment, the "broncin' buck" expression originates from "bucking bronco", a wild horse that is vicious and difficult or impossible to break in, where "bronco" means an unbroken or imperfectly broken mustang and to buck means to resist.
As a noun, "buck" may also mean a male deer, antelope, etc., a stallion included.
—Don McLean might have reversed "bucking" and "bronc" to rhyme with "truck"
https://ell.stackexchange.com/questions/12021...—A bronco is an untamed horse.
To buck is when a horse jumps and twists to try to get someone off his back. So a bucking bronco is a wild horse trying to throw the rider off his back.
—He was a wild and aggresive hormone driven teenager.
https://forum.wordreference.com/threads/bronc...BRONCING=Comes from BRONCO, that is a wild horse from North America.
BUCK=male of some animals.
https://answers.yahoo.com/question/index?qid=...