Justin Masterson, American baseball player
Justin Daniel Masterson (born March 22, 1985) is an American former professional baseball starting pitcher. Drafted by the Red Sox in the second round of the 2006 MLB draft from San Diego State University, he made his MLB debut two years later. Masterson also played in MLB for the Cleveland Indians and St. Louis Cardinals. Known for primarily throwing a sinking fastball, the right-hander stands 6' 6" (198 cm) tall, and weighs 250 lb (113 kg).

A former All-Star selection, Masterson placed in the top-ten in the American League multiple categories in 2013, including wins, strikeouts, complete games, hits per nine innings pitched, and strikeouts per nine innings pitched. He was the first Red Sox pitcher since Fenway Park's 1912 opening to make his first four consecutive starts there and not lose any of them.