Sylveanus Augustus "Vean" Gregg (April 13, 1885 – July 29, 1964) was an American professional baseball player.

A pitcher, Gregg played in Major League Baseball (MLB) for the Cleveland Naps, Boston Red Sox, Philadelphia Athletics, and Washington Senators from 1911 through 1925.

Gregg led the American League in earned run average in 1911 and was on the roster of the Red Sox when they won the 1915 World Series, but did not appear in any games.

[2] The next year, Gregg played for the Cleveland Naps of the American League, pitching to a 23–7 win–loss record with a league-leading 1.80 earned run average.

On December 14, 1917, the Red Sox traded Gregg, Merlin Kopp, Pinch Thomas and $60,000 to the Philadelphia Athletics for Bullet Joe Bush, Wally Schang, and Amos Strunk.

After the 1924 season, Seattle sold Gregg to the Washington Senators of the American League for three players and cash considerations.

After his playing career ended, he owned and operated The Home Plate, a combined café and sporting goods store in Hoquiam, Washington.