Diamondbacks' Justin Upton may be as good as he'll ever be

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Here is a filthy secret about young stars: They don't generally improve. Baseball fans have it in their minds that a player will, at 27, be a better version of the player he was at 21. On average, that's true. This chart, for example, is a bit technical, but shows that the typical hitter will, at 27, be about 10 percent more valuable per plate appearance than he was when he was six years younger.

What defines a great player, though, is that he isn't anything like an average one. And Justin Upton is a great player, or close. Two years ago, when he was 21, he hit .300/.366/.532, good for an adjusted OPS of 129. In the last 30 years, just eight other hitters have done as well by that age: Alex Rodriguez, Albert Pujols, Ken Griffey Jr., Tim Raines, Rickey Henderson, Jason Heyward, Miguel Cabrera and... Tom Brunansky. That's five players who are or one day will be in the Hall of Fame, one who's on course to join them, a player who turned 21 in August, and... Tom Brunansky. Upton's prospects are obviously high.

A general manager ringing Towers to offer up his entire minor league system for Upton, though, isn't concerned with what he did in 2009, but in what he'll do through 2015, the year through which the young man is signed for the bargain sum of $49.5 million. (By way of comparison, the Houston Astros owe Carlos Lee $37 million just for the next two years, and he's terrible.) This is where the filthy secret comes in: Upton isn't likely to be much better than he's been.

Take our other young stars as guides to what may be in store for the lucky owner of Upton's contract over the next five years. From ages 23 to 27, Rodriguez's adjusted OPS of 153 was actually lower than the 160 mark he posted at 20. Griffey, Raines and Henderson all hit basically the same at those ages as they did at 21, while Brunansky hit much worse. Only Pujols and Cabrera hit new levels.

None of this is of course any knock on these players. Once you're hitting like a Hall of Famer, there is no real improvement you can make, unless you're Albert Pujols and thus capable of hitting like Mickey Mantle rather than Hank Aaron. (Scoop: St. Louis has a good first baseman.) The point is just that you can't expect the kind of linear improvement from a historically talented player that you can from a merely excellent one. Baseball is hard, and going from great to greater is in many ways harder than going from good to great.

Setting lower sights, we see a similar pattern. Juan Gonzalez, Jose Canseco, Delino DeShields, Andruw Jones, Cal Ripken Jr., Gary Sheffield and Adrian Beltre all posted adjusted OPS marks between 116 and 121 at age 21. Of them, three -- Canseco, Gonzalez and Sheffield -- were markedly better at 23 to 27. Another three -- Beltre, Jones and Ripken -- held their levels. And one, DeShields, was much worse, though his early returns made him worth trading for a young Pedro Martinez, a sort of fame worth having.

All told, of these 14 players, five improved on their youthful glory through age 27, two declined, and seven did more or less what they'd already done. This has an obvious relevance where Upton is concerned. Just going by crude odds, over the next five years he'll probably be something like a .300/.370/.530 hitter. That's very, very good. It's actually even better than it looks: He's a fine defender and a solid baserunner, and a hitter that good has decent odds in any given year of reaching truly MVP-level play. But it also presents the Diamondbacks an opportunity.

Just as most baseball fans have it in their minds that a player who was great at 21 will be much greater at 27, so presumably do some executives. If Towers can find one both willing and (the tricky bit) able to pay for Upton as if there are cinch odds that he'll follow the Pujols trajectory, he might do well to move his stud while his market value is even higher than his already frighteningly high real world value.

What makes this still more interesting and chancy is that Upton has a signal flaw, which is that he strikes out a lot. Twenty-six per cent of his career plate appearances to date have ended in a long walk back to the bench, and his walk-to-strikeout ratio is an unimpressive 0.41. This hardly tells doom for him, but it's very difficult to sustain the batting average needed to be a truly elite on-base threat (and so a truly elite hitter) while striking out more than a quarter of the time. And as it happens, the only player among those named who struck out nearly as often through age 22 was Canseco, who, along with Gonzalez and Rodriguez, was also one of just three players with a worse walk-to-strikeout rate.

This isn't wholly bad. Both Canseco and Gonzalez were among those who radically improved on early success. Canseco posted a 116 adjusted OPS at 21, and a 154 from ages 23 to 27 (an achievement of admittedly dubious legitimacy, given that this is Jose Canseco), while Gonzalez went from 121 to 137. There is also a line of thought holding that a young player who is successful despite a high strikeout rate is a good candidate for improvement, just because he has an obvious way to get better.

Still, it's exceptionally rare for a player who strikes out in nearly a third of his at-bats, as Upton does, to even have a significant major league career, let alone become a true superstar. This might count as yet another reason for Towers to deal if a team is willing to give him what he wants for Upton. What is that? "Everything," an Arizona executive tells SI.com's Jon Heyman. If they're willing to come down just a touch, the Diamondbacks might find a deal worth taking. If not, having an awesome young player locked up for five years at about two-thirds what the Chicago Cubs will pay the appalling Alfonso Soriano for the next four will make for fine consolation.