Highlighting the 10 Most Underrated MLB Players of the 2015 Season

Mike Trout. Clayton Kershaw. Bryce Harper. Superstars always get more attention for their exploits, and rightfully so.

But with the 25-man roster that MLB teams deploy, there can't be success without standout seasons from unheralded players. Over the next few slides, we'll identify the 10 most underrated players of the 2015 season. 

This was no easy task. Like most years, plenty of players have come out of nowhere to make significant impacts on their teams. Whether it's veterans like John Lackey and Curtis Granderson or rookies like Chris Heston and Jung Ho Kang, the following names have been instrumental for their clubs in 2015.

That's really the main criteria. Take away the stars who are supposed to carry their teams, and the following players are at the top of the list in terms of importance this season. 

Make sure to let your voice be heard in the comments section below. Did we leave anybody out? Do you agree with our selections? 

Before we dive into the top 10, let's take a look at some deserving honorable mentions who just missed the cut. 

Honorable Mentions

Charles Rex Arbogast/Associated Press

Logan Forsythe has been critical for a feeble Tampa Bay offense.

There has been no shortage of underrated players in 2015. In no particular order, here are a few who just missed the cut. 

• Shelby Miller, Atlanta Braves
• Jose Quintana, Chicago White Sox
• Nolan Arenado, Colorado Rockies
• Lorenzo Cain, Kansas City Royals
• Justin Turner, Los Angeles Dodgers
• Jon Niese, New York Mets
• Brett Gardner, New York Yankees
• Justin Wilson, New York Yankees
• Jared Hughes, Pittsburgh Pirates
• Joe Panik/Matt Duffy, San Francisco Giants
• Kevin Siegrist, St. Louis Cardinals
• Randal Grichuk, St. Louis Cardinals 
• Logan Forsythe, Tampa Bay Rays
• Nate Karns, Tampa Bay Rays
• Yovani Gallardo, Texas Rangers
• Mark Buehrle, Toronto Blue Jays

10. Josh Fields

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Josh Fields has been a huge part of Houston's late-inning mastery in 2015.

2015 Stats: 4-1, 43 G, 2.20 ERA, 11.85 K/9, 5 HLD

As we approach September, the Houston Astros remain in first place in the American League West. 

There's more than one reason why Houston has pulled off such a turnaround in 2015, but none has been as important as an improved bullpen. In 2014, Houston relievers recorded the worst ERA in baseball. This season, the Astros have lowered that mark by more than two full runs and rank fourth in MLB. 

The signings of Luke Gregerson and Pat Neshek have been instrumental to Houston's success, but an argument can be made that Josh Fields has been the Astros' top late-inning option.

Fields leads all Houston relievers in WAR and touts a 2.20 ERA in 43 appearances. The right-hander has been a strikeout machine in 2015, fanning over 33 percent of the batters he's faced. 

The 30-year-old's fastball has been his weapon of choice, and it's held opponents to a .168 average. He's not throwing it any harder than he did last season, but Fields has seen a jump in his chase rate. That improvement indicates he's using his heater wisely when he's ahead in the count. 

His recent demotion to Double-A was logistics based, as Houston needed to freshen its bullpen after an extensive workload this week. But make no mistake, the Astros bullpen would be nowhere near as potent without Fields and will need him for the final month. 

9. Ken Giles

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The Phillies have found their present and future closer in Ken Giles

2015 Stats: 5-2, 54 G, 1.69 ERA, 53.1 IP, 11.64 K/9, 8 SV, 12 HLD

From one reliever to another—this time we're looking at Philadelphia Phillies right-hander Ken Giles. 

Despite Philadelphia's record, Giles has been one of the club's few bright spots in 2015. The 24-year-old has built off a 1.18 ERA last year and has evolved into one of baseball's top young closers.  

Serving primarily as the Phillies eighth-inning man, Giles has dominated opposing hitters. His 1.69 ERA is good for 11th in MLB while his 11.64 K/9 ranks 14th. 

Giles didn't assume the closing duties in Philadelphia until after Jonathan Papelbon was dealt to the Washington Nationals. Since then, he's saved eight ballgames.

With a fastball that sits in the upper 90s and a wipeout slider that's generating strikeouts nearly 50 percent of the time, it's obvious Giles has the stuff to lock down games for the Phillies for years to come. 

Giles still has plenty to prove, but his dominance cannot be ignored simply because his team isn't very good. His emergence as one of the game's most promising young closers is an important development for a Phillies team suddenly headed in the right direction. 

8. Hector Santiago

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The Angels would be in a tough spot without Hector Santiago's production this season.

2015 Stats: 7-7, 2.91 ERA, 145.1 IP, 8.36 K/9, 2.87 BB/9

The Los Angeles Angels are still hanging around in the AL West despite various issues in the starting rotation. C.J. Wilson and Jered Weaver have each missed time with injuries, while 2015 breakout star Matt Shoemaker was recently optioned to Triple-A. 

Thankfully for the Halos, Hector Santiago has been a consistent, calming force in an otherwise chaotic rotation. 

Santiago posted a sub-4.00 ERA in 24 starts last season, but he has really picked up his game in 2015. The southpaw has a 2.91 ERA in 24 starts. He's improved his strikeout percentage, while walking fewer hitters as well. 

The 27-year-old spent most of his career in the Chicago White Sox farm system, culminating in 23 starts for the club in 2013. That opportunity not only allowed teams to see what Santiago could do as a starter but also gave him the confidence to know he could succeed getting the ball every fifth day.

Santiago told Vinnie Duber of CSN Chicago:

"

Those guys, they gave me the opportunity to actually start. I was in the closer role my first year, and they gave me the opportunity to become a starter. And they made it possible for me to come over here to the Angels and get a full-time job because they gave me 150 innings one year when I had 20-plus starts in a season. I never had a full-time (starting role), I didn't come out of spring with these guys as a starter, but they got my feet wet and they put me in the door so I could become a starter later on in my career. So thank those guys for that. They started me off getting into the rotation.

"

Despite Santiago's fine season, the Angels haven't been able to catch the Houston Astros in the division. Just imagine where L.A. would be without him. 

7. J.D. Martinez

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J.D. Martinez has been a steady force on a chaotic Detroit club.

2015 Stats: .287/.351/.552, 32 HR, 81 RBI, 73 R, .903 OPS

The Detroit Tigers never lived up to the hype this season. Injuries to Miguel Cabrera and Victor Martinez and the deadline trades of Yoenis Cespedes and David Price have all but ended Detroit's playoff hopes. 

But throughout all the injuries, trades and dugout skirmishes, J.D. Martinez's bat has remained a constant in a chaotic Tigers clubhouse. 

Dating back to his days with the Houston Astros, Martinez's power has never been questioned. Martinez broke out with a 23-homer, 76-RBI campaign last season, but there were questions regarding if he would be able to duplicate those numbers in 2015. 

The 28-year-old has done that and more. He's mashed 32 homers and is on pace to drive in over 100 runs for the first time in his career. Martinez ranks in the top 10 among American League hitters in WAR, homers, RBI, runs scored, isolated power, slugging percentage and wRC+. 

Not bad for a player released by the Astros before the 2014 season. 

Martinez's phenomenal year may be an unwanted consolation prize in an otherwise disappointing season. But Detroit has found something in the powerful outfielder, and he's quietly been one of the game's top hitters in 2015. 

6. A.J. Pollock

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A.J. Pollock has put together one of the best seasons of any outfielder in baseball.

2015 Stats: .321/.374/.493, 13 HR, 54 RBI, 86 R, 32 SB, .868 OPS

A talented core of Arizona Diamondbacks position players has only gotten better in 2015 as outfielder A.J. Pollock has emerged as one of the game's most complete players. 

Did you know that Pollock ranks fourth in MLB in WAR this season? The 27-year-old is ahead of names like Buster Posey, Joey Votto, Anthony Rizzo, Yoenis Cespedes, Nelson Cruz and Andrew McCutchen. 

Offensively, Pollock is hitting well over .300 with an on-base percentage over .370. He has also flashed some pop, going deep 13 times and slugging over .490. Oh, yeah. He's swiped over 30 bags this season. 

There's not much Pollock can't do at the dish, which already separates him from most major leaguers. Factor in his elite defensive metrics and it's clear why Pollock's WAR is so high. He ranks fourth among MLB center fielders with 10 defensive runs saved. 

Paul Goldschmidt's shadow can loom large in Arizona, but Pollock has established himself as one of baseball's top center fielders in 2015. If he continues to produce at this level, he won't be underrated for too much longer. 

5. Curtis Granderson

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Before the New York Mets brought in reinforcements at the deadline, Curtis Grandson was keeping the offense afloat.

2015 Stats: .253/.344/.455, 22 HR, 53 RBI, 67 R, 10 SB, .799 OPS

On the surface, Curtis Granderson's numbers don't stack up with some of the other position players on this list. He's barely hitting over .250 and has an on-base percentage below .350. 

But before the New York Mets bolstered their offense at the trade deadline, Granderson was keeping it afloat.

Granderson has played in every game for the Mets this season. He leads the team in WAR, homers and runs scored. While his average isn't all that impressive, he's hitting the ball hard over 36 percent of the time. His 12.7 percent soft contact percentage also ranks in the top 20. 

Like Owen Watson of Fox Sports put it earlier this week, Granderson's production in 2015 has been crucial for an offensively challenged Mets team:

"

The impact of his resurgence on the Mets' offense can't be overstated. With a power-starved lineup, Granderson has been the spark at the top and middle of the lineup that New York has sorely needed. Along with his contributions on the basepaths, his solid defense this season has led him to the top of the leaderboard for Mets players in Wins Above Replacement, a place he will most likely occupy at season's end.

"

While an argument can be made that Granderson is essentially the best of a bad bunch of Mets hitters, his work this year must still be applauded. New York's fantastic rotation gets most of the love, but Granderson is a big reason why the Mets are in first place. 

4. John Lackey

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John Lackey's veteran presence has been vital for St. Louis after Adam Wainwright's season-ending injury.

2015 Stats: 10-8, 2.99 ERA, 165.2 IP, 6.68 K/9, 2.12 BB/9 

The St. Louis Cardinals were dealt very bad news when Adam Wainwright suffered a serious Achilles injury in late April. 

While losing Wainwright obviously hurts, the Cardinals rotation has scooted right along. In fact, St. Louis starters have the lowest ERA in baseball this season. 

Michael Wacha, Lance Lynn and Carlos Martinez all have a sub-3.00 ERA, but an argument can be made that John Lackey has been the Cards' most important starter.

At 36, Lackey is putting together another fine season. The right-hander has a 2.99 ERA in 25 starts and leads the team in innings pitched. Lackey has been a steady customer for a St. Louis rotation filled with relative inexperience.

"Lackey is a big piece, we knew that going in whether Waino was here or not," manager Mike Matheny told B/R's Anthony Witrado in June. "We knew we needed another veteran presence in our staff, a guy who can go out there and be a stopper and rack up big innings."

Considering Lackey is pitching for the league minimum this season, there's not a pitcher with better value in MLB. Lackey has pitched well throughout 2015, but his veteran presence has made all the difference for the rest of the St. Louis rotation.

3. Jung Ho Kang

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Jung Ho Kang has proved to be well worth the four-year, $11 million contract he signed this winter.

2015 Stats: .287/.360/.444, 10 HR, 43 RBI, 47 R, 5 SB, .805 OPS

The Pittsburgh Pirates signed Jung Ho Kang to a modest four-year, $11 million deal this offseason. Kang had made a name for himself in Korea, but there were questions regarding how quickly the 28-year-old would be able to adjust to the major leagues. 

Kang has answered those concerns with a fantastic rookie season for the Pirates. In fact, a case can be made that he's the most important player on the Pittsburgh roster in 2015. 

After spending most of his playing time this season at third base, Kang has taken over the shortstop duties after an injury to Jordy Mercer. Kang ranks second among MLB shortstops in WAR, first in on-base percentage and fourth in slugging percentage. 

Pirates general manager Neal Huntington recently told Joe Lemire of USA Today that Kang has far exceeded his expectations:

"

It’s one thing to go from rural to city. It’s another thing to go from one foreign language to another. It’s another thing to go to a completely different culture based on a completely different alphabet and structure. We knew he was intelligent. We knew he loved to play the game. And we knew he loved to compete. But he has exceeded our expectations in terms of how easily he’s made the transition from Korean culture to American culture, from Korean baseball to American baseball [and] the speed of the game.

"

Because of Kang, the Pirates have been able to overcome injuries to Mercer and Josh Harrison and remain in the playoff hunt. He's produced wherever he's played and has given Pittsburgh another dependable bat to pair with Andrew McCutchen and Starling Marte. 

Kang has been a key to Pittsburgh's emergence as a dark-horse World Series contender, and he'll be crucial if the Pirates are to win it all. 

2. Chris Heston

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While the San Francisco rotation has been in flux, rookie Chris Heston has stepped up behind ace Madison Bumgarner.

2015 Stats: 11-7, 3.34 ERA, 145.2 IP, 6.80 K/9, 2.97 BB/9

How about the competition for National League Rookie of the Year this season? There are a handful of deserving candidates in which an argument can be made.

That includes San Francisco Giants right-hander Chris Heston, who has been vital for the rotation behind ace Madison Bumgarner.

In 2014, Heston posted a 3.38 ERA in 28 starts at Triple-A. That consistency has trickled into 2015, where the right-hander is 11-7 with a 3.34 ERA in 24 starts this season.

Heston's success isn't because of elite velocity or strikeout numbers. He's fanning less than seven hitters per nine innings and hasn't exceeded 93 mph this season.

Despite a lack of swing-and-miss stuff, Heston is just outside MLB's top 10 in ground-ball rate. Furthermore, Heston also ranks 12th in limiting hard contact percentage. The 27-year-old throws strikes and generates soft ground-ball contact. That'll work in the spacious AT&T Park.

The Giants have used nine different starters this season. Other than the fantastic Bumgarner, Heston is the only one that's posted a WAR above 1.0. Without him, San Francisco's chances of repeating as World Series champions would have already been lost.

And though he was sent down to Triple-A on Friday for what Bruce Bochy called a "breather," per John Shea of the San Francisco Chronicle, Heston will surely play a role for the Giants in September. 

1. Jake Arrieta

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Jake Arrieta has quietly become one of baseball's best right-handers.

2015 Stats: 15-6, 2.30 ERA, 168 IP, 9.11 K/9, 2.25 BB/9 

The Chicago Cubs have been one of the best stories in MLB in 2015. Behind a bevy of talented young position players, the Cubs seem destined to end their playoff drought. 

But the most underrated player on the Cubs and in MLB has quietly emerged as Chicago's ace: Jake Arrieta. 

It is Arrieta, not Jon Lester, that finds himself atop most MLB leaderboards this season. The right-hander is tied for first in wins, ranks fourth in baseball in ERA, ninth in innings pitched and 17th in strikeouts per nine innings.

Is this the same Arrieta who posted a 6.20 ERA in 18 starts for the Baltimore Orioles in 2013? Well, yes and no. The 29-year-old has significantly altered his repertoire, featuring his sinker and slider as his primary pitches.

As Jay Jaffe of SI.com mentioned recently, that change in offerings has resulted in the highest ground-ball percentage of Arrieta's career:

"

Where Arrieta was throwing about as many four-seamers as sinkers during his days with the Orioles, he’s now throwing the sinker 2.3 times as often as the heater and is throwing fewer fastballs in general, with his rate of sliders nearly doubling. With virtually all of his pitches, he's generating higher ground-ball rates and yielding lower batting averages and slugging percentages—dramatically lower, in some cases:

"

What Arrieta has done in 2015 is no fluke. He's always had strikeout stuff, but he's finally refined that velocity and movement into a package that works best for him. 

It works for the Cubs, too. While Lester has been frustratingly inconsistent in 2015, Arrieta has been a rock for the Chicago rotation and has thrown his hat into the ring for a potential NL Cy Young Award. 

Stats courtesy of FanGraphs and accurate as of Aug. 22.