Last year saw something of a deviation from tradition when the National League Rookie of the Year was crowned. Philadelphia’s Ryan Howard may have won the award with impressive numbers, but he only played about half a season, the beneficiary of a Jim Thome injury. This was also the case with the runner-up, Atlanta’s Jeff Francoeur, who had to wait for a series of early Braves injuries to get his chance. Historically, the award has gone to rookies who played close to a full major league season. As it stood, very few strong rookies broke camp with the major league club in 2005, and awarding a Rookie of the Year based on a partial season was a necessity.

This year, it’s a different story in the National League, as many first-year players were handed starting jobs right out of the gate and figure to get the lion’s share of playing time through the season. Even though it’s June, it’s never too early to try and pin down full-season storylines, so here’s a watch list for early NL Rookie of the Year contenders.

The state of Florida isn’t known for its youth, but Hanley Ramirez represents the first of four current Rookie of the Year candidates from the Marlins. Ramirez was Baseball Prospectus’s 33rd-best prospect in 2003, but went unranked in 2004, was ranked 24th in 2005, and finally received an Honorable Mention in 2006. The fluctuation describes his inconsistency to date, which was a major reason he was accused of being an over-hyped, good-but-not-great player while in Boston.

There was some concern about Ramirez’s ability to control the strike zone, but he’s hitting a robust .293 AVG/.364 OBA/.446 SLG, demonstrating the ability to hit for average and power (though he has five triples, which are generally are the result of speed, padding his SLG total). His pitch selectivity has also quieted critics: Among players on pace to qualify for the batting title, Ramirez is 10th in pitches seen per plate appearance with 4.12. He’s probably playing a bit over his head, but since there are no other alter natives who could force him out of the lineup, he’s likely to stay in contention the rest of the season.

Ramirez’s teammate and middle infield partner Dan Uggla was a Rule 5 selection from Arizona, where he toiled in the minor leagues for five years and never made it higher than Double-A. At 26, Uggla is a bit long in the tooth to have a strong season mean there’s more development to come, but you’ve got to tip your cap to him. There was an opening in the infield, he earned it, and he’s played exceptionally well so far, hitting .310/.359/.502.

Can he keep it up? Some warning signs suggest he won’t. His minor league track record did not portended he’d hit this well, so his place in the rankings is already more than a bit surprising. For one, his career minor league line of .276/.347/.443 takes advantage of three things: 1) he was always old for his leagues, 2) he repeated levels often, and 3) he played in the Arizona system, which is made up of hitters’ parks. Now that he’s playing for the Marlins – whose home park is traditionally friendly to pitchers – his production seems even more out of character. Uggla is a great bet to regress as the season progresses, dropping him out of contention.

Marlins hurler Josh Johnson is the lone pitcher on our list, and might not be long for contention. His 2.11 ERA is exceptional, except some of his peripheral statistics suggest he can’t keep it up. For one, his hit rate is among the best in league, as only Carlos Zambrano and Pedro Martinez allow fewer hits per nine innings. This is well out of whack with the rest of his career to date, and since he doesn’t have dominant strikeout numbers the way Zambrano and Martinez do, he’s more reliant on a below-average defense to turn batted balls into outs. Add in an above-average walk rate and the fact that he’s allowed six unearned runs in 55 innings, and he’s got nowhere to go but down. Regression to the mean isn’t always a guarantee, but this doesn’t represent a new level of ability for Johnson. Proceed with caution.

It’s almost impossible to mention Milwaukee first baseman Prince Fielder without mentioning his slugging father, Cecil. There have been no shortage of appetite jokes aimed at both Fielders, but Prince has more going for him from an athletic standpoint. He’s more nimble around the first base bag than his size would suggest (he’s listed at 6-feet, 260 pounds), but he’s certainly not athletic enough to move to another position. His current batting line of .296/.352/.515 is about what he was projected to do, and he stands the best chance of slugging his way to the award, a la Ryan Howard, since everyone above him on the list is outperforming their projections by some degree.

Conor Jackson was a highly touted first baseman in the well-stocked farm system of the Arizona Diamondbacks. Like Uggla, he benefited from some offensively generous home parks in the minors. But unlike Uggla, he displayed more secondary skills to suggest he wouldn’t be overmatched once he arrived in the big leagues. Jackson has an established history of hitting for average, power, and controlling the strike zone. In fact, he finished his minor league career with a superb strikeout-to-walk ratio of 174 to 145.

Jackson had nothing left to prove in the minors before 2006,and so when the old Arizona regime re-signed Tony Clark, it effectively blocked Jackson from a starting role. Thankfully, the new regime is committed to keeping his .279/.367/.441 line on the field whenever possible. Like Fielder, he has little defensive value, but his bat more than makes up for it.

Josh Willingham has been a man without a steady position for a few years, as it’s taken him longer than expected to reach the majors. At 27, he’s the elder statesman of the Florida rookie crop. He’s long been a player with “old player skills,” namely his power stroke, his batting eye, and his passable defensive skills. That’s not a recipe for long-term success, because once one of those skills starts to go, there’s no reason to keep him around as a defensive replacement, pinch-runner, or part-timer. Willingham’s future is now, in other words. This season he’s played admirably (and cheaply) as a competent left fielder. But credit Florida with using him creatively rather than burying him in the minors for another year, as his bat is unequivocally big-league quality.

Mr. Erhardt is a writer for Baseball Prospectus. For more state-of-the-art analysis, visit www.baseballprospectus.com.