Even contenders have their flaws.  Defining contenders as any team Clay Davenport gives at least a five percent chance of reaching the playoffs and using weighted on-base average, let's identify the weakest offensive production by position in the NL.

• Catcher: Reds (.263), Diamondbacks (.265).  For the Reds, giving Devin Mesoraco the clear starting catcher role over Ryan Hanigan would boost their offensive production out of the position, but of course this position is about a lot more than hitting.  The D'Backs are in a tough spot.  They have a major commitment to Miguel Montero, and he's been brutal so far this season.  They probably just have to hope he pulls out of it.
• First base: Rockies (.289), Phillies (.317).  The Rockies have used Jordan Pacheco, Todd Helton, and a little bit of Michael Cuddyer at first base this year.  In theory, the Rockies could go with Cuddyer at first and someone like Tyler Colvin in right field.  The trade market is bleak at the position, as Justin Morneau and Carlos Pena would not be clear upgrades for Colorado.  Corey Hart could be an interesting option, once he comes off the DL.  The Phillies owe Ryan Howard roughly $98MM through 2016, so they'll just have to hope he can start drawing some more walks and begin to add positive value.
• Second base: Nationals (.227), Diamondbacks (.284).  Second base has been a black hole for the Nats, with Danny Espinosa and Steve Lombardozzi struggling.  Fans are calling for the return of 2011 first-round pick Anthony Rendon, but he probably needs to gain more experience at second base first.  The D'Backs have used Martin Prado at second baes a decent amount in Aaron Hill's absence.  Should Hill require surgery on his hand fracture, perhaps the D'Backs will look into an acquisition.  Maybe third base prospect Matt Davidson, hitting .311/.342/.544 at Triple-A this month, could help the situation.
• Shortstop: Dodgers (.219), Pirates (.248).  Hanley Ramirez should return from a hamstring injury next week, providing a lift to the Dodgers' abysmal offensive production at shortstop.  The Pirates signed Clint Barmes in the 2011-12 offseason for his defense, but it barely makes up for the automatic outs at the plate.  Jordy Mercer, John McDonald, and Chase D'Arnaud aren't much better, and highly regarded prospect Alen Hanson is still at High A.  Good luck finding a decent-hitting shortstop on the trade market, though.  The White Sox, should they drop out of contention, could offer up Alexei Ramirez at a premium.
• Third base: Pirates (.259), Rockies (.280), Dodgers (.288).  It's been a power-only show for the Pirates' Pedro Alvarez at the hot corner, as he's striking out a ton and owns the fifth-worst qualified OBP in the NL (.257).  Aramis Ramirez would be a fun pick-up, though intra-divisional trades can be tricky.  Chase Headley would be a huge addition, but only if the Padres are willing to listen.  The Rockies will give rookie Nolan Arenado some time to find his footing.  Less Luis Cruz should be enough to give the Dodgers a lift.
• Left field: Diamondbacks (.300), Reds (.300), Giants (.302).  The D'Backs have used six different left fielders, and figure to stick with Jason Kubel and Cody Ross.  With Ryan Ludwick and Chris Heisey on the DL, the Reds have been employing Xavier Paul of late, and he's been solid overall.  The Giants' combo of Gregor Blanco and Andres Torres was never meant to be offense-first, and Torres has heated up in May anyway.  Should one of these teams turn to the trade market, Josh Willingham, Carlos Quentin, Michael Morse, Jason Bay, Raul Ibanez, Melky Cabrera, and Alfonso Soriano are some candidates.  Several of those players don't work for the Giants, however.
• Center field: Dodgers (.278), Braves (.278), Phillies (.288).  Center field is not an offense-first position, but in general these teams just need to get more out of their incumbents.  Matt Kemp might miss some time with a hamstring strain, which could allow for Joc Pederson to get a look with the Dodgers.  It seems crazy for the Braves to push B.J. Upton into a full-blown platoon with Jordan Schafer months after committing $75.25MM over five years, but that could be an option at some point.  The Phillies were looking mostly for defense from Ben Revere, but .263/.302/.294 is still tough to stomach.  John Mayberry Jr. can pitch in a bit.  As for the trade market, Peter Bourjos, and Franklin Gutierrez could become available when healthy.  David DeJesus, Chris Coghlan, and Alejandro De Aza could also be options.
• Right field: Phillies (.294), Braves (.313).  Delmon Young hasn't done much for the Phillies in right so far.  The Braves' Jason Heyward has been terrible, and we'll see how long they can wait that slump out.  Trade options could include Giancarlo Stanton, Alex Rios, Andre Ethier, Nate Schierholtz, Chris Denorfia, Morse, and Hart.

The non-tender deadline is December 2nd this year, a mere six months away.  Let's take a look at some arbitration eligible players who might be on the chopping (or at least trading) block before then due to the combination of rising salaries and lackluster performance.

• Ike Davis, Mets.  If Davis doesn't turn things around this year, what will the Mets do in the offseason?  One thing about a player having a terrible year is that he doesn't get a big arbitration raise afterward.  So if Davis' salary for next year is to remain below $4MM, the Mets would at least be able to find a team willing to see if a change of scenery helps.
• Clayton Richard, Padres.  The pitch-to-contact thing doesn't work so well when you also walk a bunch of guys and over 30% of your flyballs leave the yard.  Richard is earning $5.24MM, and should his struggles persist, I imagine the Padres would not bring him back even at the same salary.
• James McDonald, Pirates.  McDonald's velocity is down, and walks have been a problem.  He's at $3.25MM this year and sports a 5.76 ERA.
• Luke Hochevar, Royals.  This is a tricky one.  Hochevar's move to the bullpen has gone well, but will the team want to commit $5-6MM for a reliever in 2014?
• John Axford, Brewers.  Axford quickly lost his closer job again and has a 6.33 ERA on the season.  The silver lining is that he is unscored upon in his last seven appearances.  Axford's save totals have gotten him to $5MM already, and even if he doesn't add any more this year and keeps pitching well, it will be a tough call to retain him through arbitration.
• Chris Perez, Indians.  Similarly, saves have gotten Perez up to a $7.3MM salary.  He's struggled with walks this year and is currently on the DL with shoulder soreness.  If he comes back, pitches OK, and adds some more saves, the Indians might have a hard time committing $8MM+ for 2014.  Perez would probably be more of a trade candidate than a non-tender candidate.
• Ryan Roberts, Rays.  Already earning nearly $3MM, Roberts has a .236/.288/.364 line so far.
• Jeff Niemann, Rays.  Niemann had shoulder surgery in April, and the Rays will be forced in December to decide whether his 2014 season might be worth $3MM.
• Alfredo Aceves, Red Sox.  Aceves survived last year's non-tender deadline and scored a $2.65MM salary, and the team wasn't able to trade him.  A 6.57 ERA so far in 2013 earned him a demotion today, so he might not make it to the non-tender deadline.
• A few more non-tender candidates to consider: Nolan Reimold, Emilio Bonifacio, Roger Bernadina, Chris Heisey, Chris Getz, Brennan Boesch, Sam Fuld, John Lannan, Marc Rzepczynski, and Chris Volstad.
• Plenty of other arbitration eligible players probably aren't non-tender candidates, though their teams could be reluctant to pay them higher salaries through arbitration.  A few names that come to mind in this bracket include Rick Porcello, Alex Avila, Tommy Hanson, Pedro Alvarez, Ivan Nova, Phil Coke, and Mitchell Boggs.  Some of these players could become trade candidates if their current teams prefer not to pay them next year.