MLB trade rumors: Who are the biggest upgrades by position for contending teams?

The MLB trade deadline is one of the most exciting times of the year on the baseball calendar. Contenders are doing everything they can to position their clubs for a stretch run and postseason glory, while the also-rans are jostling for prospects by selling off talented players that don't fit into their future plans. The trade deadline is all about correcting mistakes and marginalizing weaknesses that may or may not have persisted since the offseason.

We have already seen a couple of deals to plug major holes. The Boston Red Sox struck a deal for starter Drew Pomeranz, filling a major void in their starting rotation. Now, the Chicago Cubs are on the verge of acquiring Aroldis Chapman to fix one of their few flaws.

There are still plenty of other clubs out there with needs, though. Today, we are going to examine the biggest holes in baseball among contending teams, and find the best possible replacement on a selling team for that contending club.

To determine the projected upgrade for each deal, I took the difference of the rest-of-season Steamer projections for the player to be traded and the player being replaced. Keep in mind that these projections (a) are typically conservative, especially for top talents, and (b) are prorated over roughly 60-70 games in tightly contested playoff races, so even partial wins matter and small sample sizes abound. These deals are not realistic -- some of the potential upgrades may not even be available via trade -- but represent the maximum possible value a team could extract (per Steamer projections) over the last two months of the season.

Catcher

Team: Indians (-1.0 fWAR)
Upgrade: Jonathan Lucroy, Brewers (2.7 fWAR)
Projected improvement: 0.8 fWAR over Roberto Perez

Two years ago, Yan Gomes looked like the next big thing among MLB catchers. He hit .278/.313/.472 with 21 home runs, caught 32 percent of baserunners, and ranked as one of the best pitch framers in baseball. His newly signed six-year, $23 million contract already looked like a steal.

Then Rajai Davis slid into Gomes' leg on a play at the plate in April 2015, he sprained his knee, missed six weeks, and has not been the same player since. He hit just .231/.267/.391 last season and managed a 30 wRC+ in 2016 before separating his shoulder on a play at first base. Roberto Perez has proven to be a capable backup, but the Indians don't appear to be settling. They have already put in calls to the Milwaukee Brewers about Jonathan Lucroy's availability. Lucroy, a 30-year-old with a very affordable team option for 2017, would not preclude the Tribe from relying on Gomes in the future while boosting their chances at competing for a World Series this season.

First base

Team: Nationals (-0.8 fWAR)
Upgrade: Steve Pearce, Rays (2.0 fWAR)
Projected improvement: 0.0 fWAR over Ryan Zimmerman

Steamer has a lot more respect for Ryan Zimmerman than the Cubs' pitching staff did earlier this season. The 31-year-old first baseman is hitting a meager .221/.284/.402 with 12 home runs this season, a 79 wRC+ that ranks third-lowest among MLB first basemen (minimum 200 plate appearances). Only Ryan Howard and Mark Teixeira have been worse.

Fortunately for the Nats, they did not fare any worse without him while he was on the disabled list. Unfortunately for the Nats, they didn't do any better either. Clint Robinson got the majority of starts at first while Zimmerman was out, and he has equaled Zim's -0.4 fWAR total on the season. Moving Daniel Murphy to first might be their best lineup for now, though shortstop Danny Espinosa has cooled off considerably after a hot June.

Enter Pearce, who is the kind of player that could thrive on a National League roster. He plays multiple positions and hits for power, making him an excellent plug-and-play option whether he starts or pinch hits. Pearce is a pending free agent as well, so the Rays will likely look to move him before the trade deadline. He is 6-for-22 with a home run since coming off the disabled list last week and has a .923 OPS on the season.

Second base

Team: Pirates (0.8 fWAR)
Upgrade: Jean Segura (2.3 fWAR)
Projected improvement: -0.2 fWAR over Josh Harrison

Josh Harrison is actually projected to be better than Jean Segura down the stretch, which seems like a fair assessment. A lot of Segura's value comes from a .314 batting average that is inflated by a career-high .351 BABIP, and what little power he has shown has been almost exclusively at Chase Field. Harrison has cooled off recently, but was a league average hitter in 2015 and is one year removed from a five-win season. Segura has had a wRC+ in the sixties in three of his five MLB seasons.

Shortstop

Team: Mariners (-0.5 fWAR)
Upgrade: Zack Cozart (2.5 fWAR)
Projected improvement: 0.5 fWAR over Ketel Marte

Here's the thing about shortstops: good ones don't tend to become available via trade all that often. We're in the midst of a shortstop boom right now, but the majority of those budding stars are either cost-controlled, playing on a contending team, or both. In other words, Carlos Correa isn't leaving Houston anytime soon.

At 30 years old, Zack Cozart may be the exception to this new norm. He ranks ninth among MLB shortstops with 2.5 fWAR this season and is hitting a career-best .265/.317/.471. Strangely, his offensive production has improved in games outside the hitter-friendly Great American Ballpark, and seems to be perking up again after relatively cool months in May and June. He has also played his usual steady defense, ranking among the top five defensive shortstops in most advanced metrics.

While Cozart's name hasn't been thrown around in many trade circles -- again, most clubs in contention are set at shortstop -- he would be a solid trade candidate most years. He is under club control for one more year, and the Reds aren't going anywhere in 2017. They could slide Eugenio Suarez over to short for the time being, and they aren't likely to guarantee long-term money to Cozart for his age 32+ seasons anyway.

Third base

Team: Astros (0.8 fWAR)
Upgrade: Evan Longoria (3.8 fWAR)
Potential improvement: 0.9 fWAR over Luis Valbuena

If it weren't for Alex Bregman, Yulieski Gurriel, and a host of others the Astros could play at third base -- Luis Valbuena has been worth a steady 1.3 fWAR this year -- this idea would be very intriguing. There have been whispers about the Rays potentially shopping Longoria, with the Los Angeles Dodgers the likely destination should anything concrete arise. It's not likely that Tampa trades the best player in their franchise's history, but it wouldn't be a surprise to see the Rays prioritize efficiency over sentimentality.

Like the Dodgers, the Astros also have the type of talent within their system to pry a big piece like Longoria away from the Rays. Most discussions around Houston's loaded farm system center around a hypothetical trade for a front-line starter -- just imagine what Chris Sale would do to those throwback uniforms -- but they have been surprisingly aggressive in the trade market lately, and Longoria would represent a big defensive upgrade as well. They also have the roster flexibility and financial means to handle his later seasons gracefully.

Photo credit: Kim Klement-USA TODAY Sports

Photo credit: Kim Klement-USA TODAY Sports

Corner outfield

Team: Tigers (-1.9 fWAR)
Upgrade: Carlos Gonzalez (2.8 fWAR)
Potential improvement: 0.4 fWAR over J.D. Martinez

It should be noted that most of the negative value in the Tigers' outfield is actually coming from career infielder Mike Aviles, who has been shoehorned into an outfield role for reasons unknown outside the team offices on Woodward Avenue. The player being replaced in this scenario, J.D. Martinez, has actually been the Tigers' most valuable corner outfielder, at 0.4 fWAR. He was sporting a 131 wRC+ prior to suffering a forearm injury in June, and is set to come off the disabled list soon.

Meanwhile, Justin Upton is batting just .235/.290/.388 and has been 0.5 wins below replacement level. The Tigers' $132 million man has progressively improved as the season has gone on, but is still nowhere near the caliber of player we've watched over the past several years. Still, there is almost no way the Tigers would look for a replacement for either corner outfielder, and they don't have the prospects to pry Gonzalez out of Colorado.

Then there's the availability of Gonzalez himself (don't @ me, Rockies fans). He has seemingly been on the trade block for the last three years, but the organization has been reluctant to move him. With two years left on his contract and Gonzalez still healthy, now might be the best time to find a suitor, especially with how shallow the free agent market is this offseason.

Center field

Team: Astros (-0.9 fWAR)
Upgrade: Charlie Blackmon (1.4 fWAR)
Potential improvement: -0.5 fWAR over Carlos Gomez

Steamer is still optimistic about Carlos Gomez's rest-of-season prospects, but I imagine Astros fans are singing a different tune. Gomez was trending upward at one point, and hit .286/.362/.452 in June after an absolutely dreadful start to the season. However, his July numbers are NSFW, including a 3-for-26 stretch since the All-Star break. His swinging strike rate is at an all-time high, and his relatively brief peak as an above average hitter makes me think he won't amount to much down the stretch.

Of course, Blackmon isn't a huge upgrade, and probably shouldn't be patrolling center field for a contending club. However, he's under club control for two more seasons and his left-handed bat is a perfect complement to righty Jake Marisnick (who has been even worse than Gomez). Blackmon would also be a nice fit in Washington, where Ben Revere has been worth -0.6 fWAR in 61 games. Blackmon could split time with Michael Taylor and move to a corner when Jayson Werth is out of the lineup.

Starting pitcher

Team: Pirates (2.9 fWAR)
Upgrade: Rich Hill (2.5 fWAR)
Potential improvement: 1.0 fWAR over Jeff Locke

In order to add a dash of realism to this exercise, I assumed that the Pirates would not empty their farm system to chase after the likes of Chris Sale or Jose Quintana, both of whom have outperformed Hill by a few tenths of a win this year. Hill has been more valuable on a per-inning basis, though, and would be a huge boost to a Pirates starting staff that has the fourth-highest ERA in the National League.

While Hill is projected to be a full win better than Locke, it's unclear who would be displaced by an addition in real life. The Pirates just placed Tyler Glasnow on the 15-day disabled list, and may be turning to Jon Niese (-0.5 fWAR in 2016) in the meantime. Niese is projected for just 0.3 fWAR down the stretch, making Hill a 1.2 WAR upgrade on paper.

Bullpen

Team: Rangers (-0.6 fWAR)
Upgrade: Wade Davis (0.8 fWAR)
Potential improvement: 0.1 fWAR

It's a bit shocking, really. Not only do the Rangers have a 57-42 record that is percentage points away from being the best in the American League, but they have managed a 19-7 record in one-run games despite having the highest bullpen ERA in the AL. Their 5.01 bullpen ERA is "bested" only by the Cincinnati Reds, who have collectively been worth -3.6 fWAR this season (yes, just their bullpen). The Rangers have been searching far and wide for starting pitching help, but would definitely take a reliever if one fell into their lap.

Enter Wade Davis, arguably the best one of them all. Davis is tied for 26th among qualified relievers with 0.8 fWAR, but spent some time on the disabled list. He has only thrown 31 2/3 innings this season, while many top relievers have thrown at least 40 innings. If we level the playing field by looking at RE24, Davis ranks sixth among relievers, at 13.5 runs above average. It's also worth noting that he outperformed his FIP by over a full run last year as well.

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Rob Rogacki is a contributor at Beyond the Box Score and the Managing Editor of Bless You Boys, SB Nation's Detroit Tigers community. You can follow him on Twitter at @BYBRob.