Joseph John Sommer (November 20, 1858 – January 16, 1938) was an American professional baseball outfielder. He played in Major League Baseball (MLB) from 1880 to 1890 for the Cincinnati Stars, Cincinnati Red Stockings, Baltimore Orioles, and Cleveland Spiders. In 1886, Sommer set the record for the lowest single-season batting average (.209) by a player with 500 or more at-bats. His record was broken in 1888 by Al Myers of the Washington Nationals, who hit .207 that year. In the 1880s, the New York Clipper praised Sommer as one of the strongest defensive outfielders in baseball.