No team in baseball is perfect, even ones like the Baltimore Orioles and Los Angeles Angels that have more-or-less locked up their division titles several weeks before the end of the regular season. In fact, most teams have at least one player who is actively hurting the team in at least one facet of the game.
Defensively, those black holes are the players every team's pitchers hope to avoid on their allowed balls in play. At best, their defensive mistakes require pitchers to throw extra pitches and earn extra outs. At worst, they are the players who could preemptively end their teams' seasons with untimely misplays and errors, as happened with Matt Holliday and the St. Louis Cardinals in Game 2 of the 2009 NLDS.
Let's take a look at defensive concerns for potential playoff teams.
National League
Washington Nationals: Asdrubal Cabrera, Second Base
Early in the season, the Nationals played musical chairs at second base, rotating between Danny Espinosa and Anthony Rendon when Ryan Zimmerman was healthy and still primarily playing third base. With Espinosa reaching base at a .281 clip, the Nationals smartly addressed the position at the trade deadline by acquiring Cabrera from the Indians. Cabrera has provided the offensive improvement the team was looking for with a .333 OBP since the start of August. His defense is another story. Traditionally a poor defensive shortstop, Cabrera has not improved with the move to second base. In fact, the 11 runs he has cost the Nationals since Aug. 1 are the most in baseball by any player at any position.