Castro needs to be able to make the triumphant third turn more often to become a star.
When it comes to baseball prospects, age versus level is a handy, shorthand way to evaluate them. Once they reach the big leagues, contact rates and batted-ball tendencies are maybe the most useful data sabermetricians have turned out since the turn of the century.
All along, it's important to keep track of which players have substantial upside. That is, which can still improve substantially from here.
A prospect given no leeway or benefit of the doubt will be forever misunderstood and underrated. Every baseball player comes to the show with something meaningful yet to learn or with growing left to do. No one peaks, in an absolute sense, at age 23.
Ay, but there's the rub!
Simultaneously, there are a handful of young athletes every season in MLB from whom too many expect too much, simply because those guys are young and have not yet had a chance to fail. Omne ignotum pro magnificum.
It is often too tempting too dream on a guy's ceiling, rather than coolly weighing his upside against his risk of flame out or of simply settling in as a useful non-superstar.
In that spirit, here are five players whose ceilings might be lower than many imagine.
Castro is already very good. But can he ever be great?
Call it Cubs Fan Syndrome. The West Side Rooters have always been too prone to the pratfall of high expectations.
A team 100-plus years clear of its last World Series title always thirsts for the future, but the Cubs have a long line of failed prospects to show for their aggressiveness.
Castro is unlikely to truly bust. He is an even better hitter at 21 than he was at 20, and he seems to be developing some power. In the future, he could be a .300-plus hitter with average speed and 15 to 20 homers per season.
He could make 10 more All-Star teams and maybe even earn one of his future berths (he did not really deserve this one).
However, it's easy to imagine ways Castro could fall short of utter stardom. His power could develop, but right now, it's still just middling. Meanwhile, he has all the athletic tools to cover shortstop, but his hands are too stiff and his arm too erratic for him to ever be a solid player there.
He probably projects as a third baseman, and unless he (unexpectedly) finds 25-plus homer pop or learns to draw a substantial number of walks, his profile hardly makes him a superstar man at the hot corner.
Cubs fans takes refuge in Castro's greatness (18 for his last 37, on an tear and a joy to watch hit) right now but should prepare for the idea: He's not Barry Bonds, and it will take much more than Castro to even threaten the team's streak of futility.
One terrific rookie season is sometimes a good way to set oneself up for failure. Especially in rookie workloads or innings, it's easy to see some gaudy numbers but difficult to see some of a given player's important flaws.
Feliz blitzed the pro baseball ladder. His combined innings above A-ball constitute roughly four months' work for an MLB starting hurler.
By throwing a smooth, effortless fastball and by throwing it for strikes without using the middle of the plate, Feliz was able to scale the heights without fighting to refine his secondary offerings or his control.
It worked swimmingly throughout his 2010 AL Rookie of the Year campaign. However, Feliz's success acted more as a Band-Aid than as a curative ointment. No one noticed the chinks in his armor last season.
This year, it has become much more apparent that Feliz needs to improve to become an elite hurler. He simply is not putting his fastball past hitters with the same ease or regularity. And his breaking ball and change up have taken meaningful steps back.
Feliz could move into the rotation in 2012 and become a dominant pitcher. He could also become a dominant closer again. But the possibility that he would settle into a non-impact role at the back of the rotation or front of the bullpen is not illusory, and too many Rangers fans have minimized it.
White is limited by his arsenal of pitches.
A former first-round pick who reached Cleveland in less than 24 months, White became even more noted (and took an even heavier burden of expectations) after being a part of the Ubaldo Jimenez deal for the Rockies and Indians.
Here's the problem. He might never thrive as even a mid-rotation starter in the big leagues.
He has, essentially, two pitches: a fastball and a splitter. That's not merely an exceptionally rare cocktail for a starting pitcher but an almost unprecedentedly small repertoire.
He had a solid slider in high school, but it has evaporated, and Colorado is no place to try to get it back.
White could still make it—the two pitches are both above-average—but he'll need to be very fine to do it, and the order may be too tall. A move to the bullpen would add viability and durability, but obviously, it would also hurt the return on Colorado's investment.
Rockies fans should not get so excited about their new acquisition as to forget what he is and what he is not.
Upton's power stroke has been a scary sight in even cavernous PETCO Park this season.
Upton had a breakout year at a very young age in 2009, so the D'Backs rewarded him with a six-year contract.
Between those two feats, Upton got a huge helping of exposure, and he has never been back out of the spotlight for a very mercurial team ever since.
Upton is having a huge year in 2011, after a down (but not all that bad, really) 2010. Yet some continue to wonder how much better he can be. After all, they are fond of noting he's only 23 years old.
But age-based career path projections are tricky animals, and sometimes, it must be acknowledged that a given player is not going to be much better than he is at 23.
Upton is wildly athletic and has a great swing, but his pitch-recognition skills—hard to acquire if not God-given—are only average, and he plays a non-premium position.
He's likely to make some All-Star teams, but like Castro, he might fall short if people continue to whisper about Cooperstown long before they ought to be so ambitious.
Harper's hype is a bit ahead of itself.
Could Bryce Harper break all the records and retire as one of the best combinations of raw power and pure hitting ability in MLB history? It's very possible.
Could Harper settle in as more of an Adam Dunn type, a non-athlete who hits for power but swings and misses in waves and never hits .300? It's very possible.
Yet, of the latter scenario, virtually no mention is made by most gurus today. Harper, in their view, is as close to a can't-miss prospect as ever there has been.
His swing is vicious and nearly impossible to impugn. He has a rocket arm from the outfield. He runs the bases really well, although for how much longer, it's hard to say.
Harper looks for all the world like a superstar-in-waiting. But most guys like this discover it's harder than it looks to command the strike zone and still hit for power.
Jose Bautista, Ted Williams, Barry Bonds (OK, one of these things is not like the others, but these two years for Bautista have been in that echelon) and their ilk are few and far between.
Harper should aspire to those players' excellence, but being a comp for Dunn is also an admirable aim, and it seems much more feasible.