John Michael Adamson (born September 13, 1947) is an American former professional baseball player, a right-handed pitcher who appeared in eleven Major League Baseball games for the Baltimore Orioles. Adamson stood 6 feet 2 inches (1.88 m) tall and weighed 185 pounds (84 kg).
Drafted out of the University of Southern California in the first round of the secondary phase in the 1967 Major League Baseball Draft and signed to a Baltimore contract on June 27, 1967, Adamson became the first player to go straight to the Major Leagues without spending a day in the minors since the institution of the June baseball lottery in 1965. In his July 1 debut against the Cleveland Indians, Adamson hurled two innings of relief; he surrendered two hits, two earned runs, and three stolen bases, including a steal of home by Cleveland's Chuck Hinton. He would be sent to the minors after his third MLB appearance (and second start), although he would spend part of the next two seasons with the Orioles.