Sean Christopher Marshall (born August 30, 1982), nicknamed "Big Smooth", is an American former professional baseball pitcher.

[2] Marshall spent three years in the minor leagues before being promoted to play with the Cubs, and had 24 starts in his rookie season in 2006.

Marshall's twin brother Brian also plays baseball, and was taken in the fifth round of the same draft by the Boston Red Sox.

Marshall made his major league debut against the St. Louis Cardinals on April 9, 2006, recording a no-decision.

He stayed in the starting rotation for the first half of the year before suffering a strained left side muscle.

On September 2, Marshall returned to the Cubs' rotation, but posted a loss against the San Francisco Giants.

On May 22, Marshall was promoted to the Cubs' starting rotation by manager Lou Piniella replacing Ángel Guzmán.

On June 3, 2007, he claimed his first win of 2007 by matching a career high 8 strikeouts by leading the Cubs to a 10–1 victory over the Atlanta Braves.

[10] Marshall extended his string of quality starts with two additional wins against the Atlanta Braves and the Seattle Mariners, improving his record to 3–2.

[14] Marshall was traded to the Cincinnati Reds on December 21, 2011, in exchange for Travis Wood, Dave Sappelt and Ronald Torreyes.

However, due to Marshall's poor performance in the closing role, the Reds named phenom Aroldis Chapman the closer in late May 2012.