Moses J. "Chief" Yellow Horse (also Yellowhorse) (January 28, 1898 – April 10, 1964), was an American professional baseball pitcher. He played two seasons in Major League Baseball for the Pittsburgh Pirates, from 1921 until 1922. An Oklahoma native, Yellow Horse, a Native American from the Pawnee tribe, was the first American Indian to have played in the Major Leagues.

Yellow Horse was born in United States Indian Territory to Clara and Thomas Yellow Horse in the early part of 1898 (one source lists his given name as "Mose", though all other sources give it as "Moses"). Yellow Horse was a full-blooded Native American since his parents were Native Americans of unmixed ancestry. Additionally, he was ordered to attend a traditional school by the Indian Agency. It was at the Chilocco Indian Agricultural School that Yellow Horse started his baseball career. In 1917, he performed at a high level for the school, and compiled a win–loss record of 17–0.

After Yellow Horse left Chilocco, he went to pitch for the Arkansas Travelers of the minor league Southern Association. In 1920, under the tutelage of Kid Elberfeld, he helped the team to its first championship.

In 1921, Yellow Horse joined the Pittsburgh Pirates. His major league debut was on April 15 in relief of Earl Hamilton. The Pirates won the game 3–1 over Eppa Rixey and the Cincinnati Reds. Later that year, he ruptured his arm and had to have surgery. His injury forced him to sit out two months. The next year, Yellow Horse injured his arm a second time. The injury was purportedly a result of a fall he took while drunk. Over his two-year stay with the Pirates, Yellow Horse was used primarily as a reliever, and compiled a record of 8 wins and 4 losses.

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