Alice recommends Let 'er Buck!: George Fletcher, the People's Champion by Vaunda Micheaux Nelson

An exuberantly illustrated account of the Pendleton Round-Up in 1911, in which the audience disagreed with the judges' decision about who had ridden the best when the judges declared the only white finalist as the winner. George Fletcher was hailed as the People's Champion, and the audience raised money to award him a bigger purse than the official winnings. The author also included a glossary, photographs and further information about George Fletcher and the other main figures of the book, plus an excellent bibliography.
Publisher description:
African American George Fletcher loved horses from an early age. When he unfairly lost the 1911 Pendleton Round-Up to a white man, the outraged audience declared him "people's champion".