NL players to watch

Arizona Diamondbacks: Martin Prado

Prado was the key player the Diamondbacks got in return for Justin Upton in a trade with the Braves last offseason. Since playing more or less every day at a number of positions from 2009-12 in Atlanta, Prado posted a 109 adjusted OPS (100 is average). In his first year in Arizona, however, it is a meager 83. The D-Backs expected a lot more from him than they are getting, and if they intend to maintain their lead in the NL West, they will need Prado to bounce back.

Atlanta Braves: B.J. Upton

Before injuries decimated their outfield right before the All-Star break, the Braves were quite fine even with B.J. Upton failing miserably in the first year of his five-year, $75.25 million contract. B.J. himself (strained adductor muscle) joins brother Justin (calf strain), as well as Jason Heyward, Freddie Freeman and Jordan Schafer among key position players who are injured. B.J. can mitigate a lot of that lost offense by recapturing his offensive prowess from his days with the Tampa Bay Rays.

Chicago Cubs: Starlin Castro

The Cubs thought they had one of the league's future stars at shortstop in Castro, but he has significantly regressed in his fourth season in the majors. His OPS is down by more than 120 points, he isn't stealing bases with nearly the same frequency, and his defense has by many accounts gotten worse. He is only 23 years old, but the Cubs signed him through 2019 on a seven-year, $60 million extension. Castro flaming out would be devastating to the restructured Cubs, so he needs to use the second half to put himself back on the map.

Cincinnati Reds: Brandon Phillips

Phillips may be the team's top RBI guy, but he leaves plenty to be desired offensively. His current .413 slugging percentage is a career low dating back to 2006 when he started playing regularly. While he has hit plenty of home runs (12), he is only sitting on 15 doubles. Additionally, he stole 15 bases in 17 attempts last season, but has stolen only one base in three attempts this year. Phillips would be deserving of the accolades he has received this year if he were to rediscover his power and baserunning skills.

Colorado Rockies: Michael Cuddyer

The Rockies are still in it despite being four games under .500. A big reason they are even where they are is because Cuddyer is having a career year at the age of 34. His current .330 average, .391 on-base percentage and .568 slugging percentage all represent career highs, vastly exceeding his previous career bests. Some of the success is because of his home ballpark, and some of it is because of plain old luck, but the Rockies won't be able to keep up in a mediocre but highly competitive NL West if Cuddyer regresses.

Los Angeles Dodgers: Yasiel Puig

Everything turned around for the Dodgers after Puig made his major league debut June 3. Since then, they have gone 24-15, moving up from fifth place to second place while cutting into their first-place deficit by five games. Puig hit so well in a month-plus (1.038 OPS) that it merited a serious discussion about his inclusion in the All-Star Game. The Dodgers have been ravaged by injuries, particularly in the outfield, including Puig himself battling a sore hip. The Dodgers will need Puig healthy and in top form for the next two and a half months if they have aspirations to take over the NL West.

Miami Marlins: Jose Fernandez

You can watch Giancarlo Stanton, too, and you'll have exhausted all of the reasons to watch the Marlins. True, they have been playing significantly better since June than they did in the first two months, but they're still 18 games out and already making plans for 2014. Fernandez, as you may have seen in the All-Star Game, has electric stuff and at 20 years old, has a bright future as a potential ace ahead of him. Seeing him pitch once every five days is a privilege which fans of many other teams do not have.

Milwaukee Brewers: Carlos Gomez

The 2013 season has been dismal for the Brewers as they are already 18 games under .500 and 19 1/2 games out and in last place in the NL Central. One of the few pleasant surprises, though, has been Gomez. After years of fumbling around as a failed prospect, Gomez decided to toss out years of coaching advice and become a power hitter. It worked. He is setting career highs across the board and along with his great defense and baserunning, is one of the top candidates for the NL MVP award. Gomez, only 27 years old, could brighten things up for Brewers fans by taking home some hardware at the end of the season.

New York Mets: Ike Davis

If it wasn't for B.J. Upton having a terrible year, Davis would have been talked about more as he heads into the second half with an OPS barely above .500. The Mets demoted him to Triple-A Las Vegas to work on his mechanics. Under the tutelage of 51s manager Wally Backman, Davis posted a 1.091 OPS in 21 games, earning a promotion back to the majors July 5. In eight games leading up to the All-Star break, he went back to his old ways, getting only five hits (all singles) in 32 trips to the plate. Davis is only 26 years old, but the Mets can only afford to give him so much rope before they are forced to make a tough decision about his future.

Philadelphia Phillies: Cole Hamels

The Phillies will likely go into the July 31 trade deadline as buyers, as they are currently only 6 1/2 games out of first place in a very winnable NL East. They may add a center fielder to replace Ben Revere and they may add a reliever to back up Jonathan Papelbon. What they likely will not add is a starter, despite Hamels' very disappointing season in the first year of a six-year, $144 million contract. He leads the NL in losses with 11 and he has a 4.05 ERA. There is some strong evidence that his changeup -- his calling card -- is not the out-pitch it used to be, and he will have to recapture the feel for it if the Phillies want to have a second-half surge.

Pittsburgh Pirates: Jeff Locke

There is some solid evidence based on sabermetric defense-independent statistics that a lot of Locke's first-half success is fluky, based heavily on a paltry .228 batting average on balls in play. He has neither the swing-and-miss stuff nor the pristine control emblematic of most pitchers with an ERA in the 2.15 area. A regressing Locke could start another second-half swoon for the Pirates.

San Diego Padres: Everth Cabrera

Cabrera may be one of the most surprising stories of the 2013 season. He was never considered to be a future star, but he is hitting .291 with a NL-leading 34 stolen bases in 42 attempts. Naturally, there is some skepticism about his ability to keep it going over a full season, and carry it over into 2014. Cabrera could assuage a lot of skepticism by maintaining his current level of play over the final 66 games.

San Francisco Giants: Matt Cain

The Giants are in a similar position with Cain that the Phillies are with Hamels. Cain is sitting on a 5.06 ERA in the second year of a six-year, $127.5 million contract. He is only 28 years old, so his 2013 season could very well be a fluke, but his control has been at its worst over the past five years and he has been more homer-prone than at any other point in his career. A rebounding Cain in the second half would mean the Giants remain contenders in the NL West.

St. Louis Cardinals: Chris Carpenter

The Cardinals are really good. They are so good that no one player really strides ahead in terms of importance, not even Adam Wainwright or Yadier Molina. Chris Carpenter, however, is working his way back from back and shoulder issues and made his first rehab start Monday. Getting him back, whether as a starter or a reliever depending on his durability, could give the Cardinals the same boost he gave them at the end of the 2011 season.

Washington Nationals: Stephen Strasburg

Strasburg was kept out of the postseason last year as part of a predetermined plan to reduce his innings pitched. The Nationals had reached the playoffs for the first time since moving to Washington, D.C., and for the first time as a franchise since 1981, when they were the Montreal Expos. It seemed as if the assumption was that Strasburg would have plenty more postseasons in which to pitch, including 2013. The Nationals have arguably been baseball's biggest disappointment, but Strasburg can help power them into playing in October with a strong second half.

Bill Baer is a regular contributor to the SweetSpot blog. He runs the Crashburn Alley blog on the Phillies.