Oscar Martin Harrell
- Bats Right, Throws Right
- Height 6' 3", Weight 180 lb.
- School Baylor University
- Debut June 21, 1912
- Final Game June 21, 1912
- Born July 31, 1890 in Grandview, TX USA
- Died April 30, 1971 in Hillsboro, TX USA
Oscar "Slim" Harrell came out of Baylor University, where he attended in 1911-1912, to pitch one major league game in June of 1912. He pitched three innings without giving up a run, for Connie Mack's Philadelphia Athletics, who won 90 games that year. He was four years younger than teammate Eddie Collins. In the minors, he pitched for the Holyoke Papermakers and the Memphis Chickasaws.
Harrell, at 6' 3" and 180 lbs., was a natural for the nickname "Slim", which was common in the first couple of decades of 20th Century baseball. Through 2019, he is one of five major leaguers named Harrell (he was the first).