Adam Duvall, 3B, San Francisco Giants: Adam Duvall was drafted by the Giants in the 11th round in 2010 from the University of Louisville. He has been a persistent and consistent source of power in the farm system, hitting 22 homers in Low-A in 2011, 30 in High-A in 2012, and 17 more in Double-A in 2013. He's got six more homers in 23 games for Triple-A Fresno so far this year, which would project out to about 30 in a 120-game season.
I'm mentioning the power first because his other offensive skills don't stand out. He doesn't hit for high averages, running in the .250s every year since leaving Low-A (.258 in '12, .252 in '13, .256 this year). Although not radically impatient, his walk rates aren't great and his OBPs generally run around .320. Overall this year he's at .245/.316/.456 at Fresno. Of course what really matters is relative production and despite the consistency in his raw slash lines, in league-relative terms he has bounced around: wRC+ 146 in '11, 106 in '12, 114 in '13, and 99 this year.
Age 25, Duvall is a mediocre defensive third baseman and scouts aren't wild about his athletic tools. He doesn't run or throw especially well and is generally considered a fringe prospect despite his power.
Duvall does hold a spot on the 40-man roster, so he can be promoted to the majors without causing a transaction hassle. The Giants are getting virtually no offensive production out from their bench players, and Duvall's power could be attractive later in the year despite his limitations.