A comparison: Jason Heyward vs. Gregory Polanco

Before Mike Trout and Bryce Harper, there was Jason Heyward. Arriving in the major leagues at age 20 in 2010, Heyward was seen as one of the game's next huge stars. The 14th overall pick in the 2007 draft was ranked as the Braves No. 2 prospect by Baseball America at age 17. (Three of the ten on that list have played in the Pirates organization.) Heyward shot through the Braves' minor league system. In 2009 he started in High-A, demolished AA and finished in AAA winning the Minor League Player of the Year Award from both BA (the one Pirate on this list is going to surprise) and USA Today. Keith Law ranked him as baseball's overall No. 1 prospect in 2010.

Heyward was the Braves' Opening Day right fielder in 2010 and went on to post a .277/.393/.456 line with a 131 OPS+ that earned him an All-Star berth and 2nd place in NL Rookie of the Year voting behind Buster Posey. (The voting included some questionable ballots.) Injuries derailed parts of his 2011 and 2013 seasons, but in 2012 he posted an .814 OPS, 27 homers and 21 stolen bases that confirmed for many he would quickly develop into a dynamic 30-30 player as well as one of the best defensive players in the game.

The defense has been legit. Heyward won The Fielding Bible Award as MLB's best right fielder in both 2012 and 2014 (check out this video montage with Trout being victimized on the first two highlights). But the offense hasn't kept pace. In 2014 he put up a pedestrian .271/.351/.384 106 OPS+ line that included only 11 home runs in 649 plate appearances. This led to an offseason trade to the Cardinals, with Shelby Miller being the key piece going back to the Braves.

At the moment the trade looks like a grand slam for the Braves. Miller is leading the NL in ERA and has already thrown two Madduxes, and Heyward is putting up the worst offensive numbers of his career (.241/.294/.392 85 OPS+), while his defense also seems to have taken a step backward in a small sample size. Of course the Cards aren't about to give up on Heyward, but he is a free agent at the end of the season. The idea floated before the season that Heyward might be baseball's next $200 million player seems preposterous now.

I've been skeptical about Heyward for awhile:

Given current contracts & everything else I would take all three #Pirates OFs over Jason Heyward.

— David Todd (@DTonPirates) March 10, 2015

The idea that Jason Heyward is going to get a long-term deal worth $15-20 million/yr is still mind-boggling to me.

— David Todd (@DTonPirates) May 24, 2015

The next four months are going to have a huge impact on his financial future.

Gregory Polanco was much less heralded when he signed his first professional contract for $75,000, also at the age of 17, in 2009. A native of the Dominican Republic, Polanco was converted from pitcher to outfielder and didn't hit the prospect radar until 2012 when he had a breakout season in the Class A South Atlantic League, being named player of the year and the Pirates minor league player of the year. Coming into 2013 he was seen as one of the top 50-75 prospects in the game. Similarly but less impressively than Heyward, Polanco moved from High-A to AA and finished with a brief stint in AAA during the '13 season. By the end of the year he was ranked as the No. 13 overall prospect by mlb.com.

After tearing up the Arizona Fall League and getting off to a great start in AAA in 2014, Polanco made his major league debut at 22 on June 10 in right field and went on to have an incredibly impressive start to his career. He registered hits in 13 of his first 14 games, including a five-hit game, and posted a .338/.416/.441 .857 OPS in his first 78 plate appearances, which included two home runs and four stolen bases. Viewed as a plus defender with a great arm, he lacked polish in his routes, but he quickly established himself as the team's everyday right fielder.

And then it got off the rails. Polanco went into a rest-of-the-season slump and seemed to lose any semblance of the plate discipline that had been so impressive for such a young player. He hit .201/.272/.311 the rest of the way, eventually losing his starting spot and even being sent back to AAA for a short stint. During his minor league career, the left-handed hitting Polanco had shown a platoon split, but that became much more extreme at the major league level as he posted a .466 OPS with only two extra base hits in 91 plate appearances against lefties.

With that as background, let's take a look at Polanco in comparison to Heyward and where they are today. Heyward will be 26 in August. He's listed at 6'5", 245, throws and bats left-handed. Polanco will be 24 in September. He's listed at 6'5", 230, throws and bats left-handed. Their numbers on the 2015 season going into Saturday:

Virtually identical seasons to date, but the underlying numbers tell us some interesting things.

On his career, including 2015, Heyward has a .824 OPS vs. RHP and a .662 OPS vs. LHP, but in 2015, with all the SSS caveats, he has a reverse split. In 134 PAs against RHP he has a .614 OPS while putting up a .901 OPS in 46 PAs against LHP. That has to be of great concern to the Cards. Also, Heyward's ground ball rate is up significantly. Coming off three straight season with GB rates between 43-46%, he has a 58% rate this season. Other than his walk rate, down from 10.9% to 6.7%, Heyward's peripherals are largely in line with his career numbers.

Polanco hasn't yet put together a full season's worth of numbers having played in only 134 games and starting just 100 of those, but his inability to hit lefties is a concern. He has a .721 OPS in 375 PAs against righties, but a woeful .444 OPS in 116 plate appearances vs. lefties, with only two extra-base hits. It's also worth noting that his line for 2015 is almost identical to his 2014 numbers in 60% of the plate appearances. Like Heyward, there is an expectation that Polanco will develop into a 20-25 HR guy, and shots like this are the reason why, to go along with 30+ stolen bases, but to-date the power hasn't been there.

While Heyward's defense numbers aren't good this year, I'll bet that is largely noise. Polanco is still trying to find his way, but ultimately should be a plus defender. Both are very good baserunners.

Where do they go from here?

Heyward was a 6.4 bWAR player his rookie season in 2010. In 2014 he was a 6.2 bWAR player, but only 2.6 of that came from his offensive production vs. 4.8 in '10. Year-to-date he's provided 0.5 bWAR. He's under contract for $7.8 million in the last year of team control and he's had career earnings of $17.4 million. The fact that Heyward is going to potentially be a free agent in his age 26 season is tremendously unusual. Most "elite" level players are 29-31 and heading into the decline phase of their careers when they reach free agency.

Polanco was a -0.1 bWAR player last year and is a 0.7 bWAR player so far this year. He's in his first full major league season and can't become a free agent until 2021. It's reported the Pirates tried to sign Polanco to a long-term deal similar to the deals done with Andrew McCutchen and Starling Marte both last summer and again this spring but were rebuffed because of the option years being offered.

Heyward is two years older than Polanco and set to be a free agent. Polanco is tied to the Pirates for 5.5 more seasons. Clearly, because of their contracts, at this level of production Polanco is the more valuable player. But, Heyward has had success at the major league level while Polanco has yet to achieve that. It will be very interesting to see how this plays out over the rest of the season and the financial impact that these struggles, if they continue, have on the teams looking to sign them.