Duncan, 33, struggled in 64 plate appearances for the Rays after signing a minor league deal in January and making the team out of Spring Training given Scott's injury. He's shown pop at times in the Majors, slugging .430 with 33 home runs in 770 plate appearances over 2010-12. A right-handed hitter, Duncan hasn't shown a significant platoon split in his career with the Yankees, Indians, and Rays.
Shelley is the brother of former Cardinals outfielder Chris Duncan, and the son of legendary Cards pitching coach Dave Duncan. Shelley's 43 career home runs rank 14th among those born in Arizona; he's a dozen behind his brother but 105 behind all-time leader Ian Kinsler.