The Padres defense has been pretty bad this year. Not quite awful, but comfortably in the lower third of the league. This of course was part of Grand Master AJ Preller's esoteric master plan to "just hit the f'n ball." Preller's radical offseason rostermaggedon finally buried the Jed Hoyer brand of Padres baseball which revolved around lockdown bullpens, extreme run prevention defense, just enough starting pitching, and hopefully one or two runs in a game. In fairness, the Kansas CIty Royals have ridden this philosophy to some excellent baseball in the last few seasons, but years of boring baseball masquerading as "pitcher's duels" in Petco Park have lead the front office to the nuclear option on the Padres lineup - lots of bats and nowhere to play them.
On the whole, the Padres defense is only about 5.5 runs away from neutral - a seemingly fair trade for the influx of hitting talent the team acquired. While most teams are well above Fangraphs' definition of 0 defensive value added, The gulf isn't so wide as to indicate that defense is killing the Padres' chances the way some feared. However, the concern is legitimate for a team that feels like it needs to turn things around and hit its stride or depressingly settle into mediocrity. The team's defensive shortcomings have also seemingly been highlighted by the fact that the majority of the bleeding has come from the team's starting outfield trio of Matt Kemp, Wil Myers, and Justin Upton. In 109 games those outfielders have compiled more defensive "damage" than a full season of Carlos Quentin (naturally, the 2012 and 2013 seasons combined).
The biggest culprit is Wil Myers who is on pace for a peak-Adam Dunn type defensive season if he reaches 150 games in CF. It is understandable. Myers only moonlighted as a minor league centerfielder before being thrust into the role this season - which is kind of like expecting a pencil-necked poser lumbersexual to chop down an actual tree. Ostensibly, Myers could improve as the season wears on and he accumulates more experience, but so far the eye test says his defense has only deteriorated since spring. Physically, Myers is the prototype corner player. He runs well, has a strong arm, possesses lateral quickness, and good size. With the Rays he was only a slightly below average corner outfielder who really only struggled with choosing good routes while tracking fly balls. Analysis here at Gaslamp Ball has found that this problem has followed him to the west coast.
The above-linked article also took a look at Myers' limited performances in the infield - praising his instincts and lateral quickness. Though he's blocked at first base by incumbent Yonder Alonso, a move across the diamond could make sense. Such a move could add another left-handed bat to the lineup as Will Venable and Cory Spangenberg have both shown chops in center. Defensive whiz Melvin Upton is also set to return soon and could provide immediate run-prevention value as well as addressing the pressing need for a player named Melvin in the lineup. At the moment, third base has also been the least productive offensive position other than shortstop - presently nobody is worried about keeping Will Middlebrooks' bat in the lineup.
Perhaps Myers doesn't have the ability to play an adequate third base. At the moment only \Middlebrooks and the competitors for the second base job have any real experience there. There is always the possibility of Yonder Alonso, who grew up playing third base, but has been blocked by strong MLB-caliber thirdbasemen since college (Manny Machado, Danny Valencia, Scott Rolen, Chase Headley). Alonso has been a steady gloveman at first, though his footwork is sometimes on the clumsy side. He may have the tools to shift back across the diamond, but has never taken a real stab at it as a big leaguer. If Yonder was able to move to third it would set the stage for a total revamp of the team defense. One of the struggling outfielders (likely Myers or Kemp) could shift to first base and allow for a true center fielder to man the middle. Though Myers has contributed the most negative defensive value to the team, Kemp is clearly the worse defender - Myers could be close to a scratch right fielder like he was in Tampa. What if Matt Kemp's arthritis is actually just outfield defense?
This type of change would be a relatively drastic undertaking - you would have multiple players learning on the job. Players make quick transitions to first base all the time - Carlos Quentin literally can't even but he learned to play an adequate first base in only a few weeks. Third base has fewer examples of players transitioning mid-career, and even fewer outfielders becoming third basemen. However, Myers' athleticism and catching background make for an attractive "what if" scenario. Alonso himself has always maintained that third base is his natural position, but something somehow makes me want to not trust him....
Average defense in right and center, paired with even below average defense at first and third (negative 10-15 runs) would still result in a net gain of dozens of runs saved throughout the year. With wildcard contenders typically separated by only a handful of games, the idea of swapping defenders around to steal back a few runs has to be under consideration.