bust a bronco
To tame a wild horse for riding. (A "bronco" is a untrained horse or pony.) I've never busted a bronco before, and this mean old horse doesn't look too eager to let me try.
bust a bronco
to ride and thus tame a wild horse so that it can be ridden. (Bust is a nonstandard form of burst.) In them days, I made my living busting broncos. That was the meanest bronco I ever seen. Nobody could bust 'im.