As documentarian Ken Burns noted, baseball is the one game in which the defense -- not the offense -- possesses the ball. With this in mind, MiLB.com continues its "Defensive Gems" series. Over the next seven weeks, we will feature a top prospect at each position who also happens to be an elite defender. In deciding which players to focus on, this reporter polled six scouting directors and relied on his own research. After identifying a keeper at catcher, we move to shortstop, where the D-backs' Didi Gregorius, the Astros' Jiovanni Mier and the Red Sox's Jose Iglesias were narrowly edged by the Indians' Francisco Lindor.