One of the toughest issues for a baseball analyst to reconcile is when it's appropriate to start actually trusting the eyes instead of early-season projections.

But with half a season of data now under our belts, it's time to throw out the spring forecasts and start making adjustments on guys who are clearly producing beyond how we thought they would.

With that in mind, below are the five hitters who have most greatly exceeded our preseason projections in 2007:

Second Baseman, Tampa Bay Devil Rays

 Projected 2007: .262 AVG, 10 HR, $117.90
 Actual 2007: .329 AVG, 9 HR, $102.78
 Projected Rank: #24; 2007 Rank: #4

One of the first lessons you learn when putting together a forecasting system is just how volatile batting average can be. Unlike a hitter's walk rate, or even his power numbers, batting average is subject to countless factors that are beyond the hitter's control. From the ballpark a player calls home to the division rivals he faces more frequently because of the unbalanced schedule, there are many issues that affect batting average more severely than the other stat categories, and as a result, it's among the toughest numbers to project from year-to-year. Which brings us to B.J. Upton.

Like most players who outperform their preseason projection, Upton is batting for a much higher average than you'd expect, given his previous Minor (.296 average, 1,800 at-bats) and Major League performance (.251, 334). His current mark of .329 puts him the top 10 in the American League, and his batting average on balls in play (BABIP) -- a stat that tends to hover around .300 for the vast majority of hitters -- is a whopping .461, which is the highest figure in the game by more than 15 percent (min. 200 at-bats). So needless to say, the balls have been bouncing his way.

Of course, none of this means he's due for an immediate decline. While it's more likely than not that his average will drop in the second half, Upton features a broad skill-set and impressive wheels -- two factors that not only make him unique, but also allow him to maintain higher BABIPs than the vast majority of players. Conventional wisdom might peg him for an imminent collapse, but a closer look at his profile suggests a more mild decline.

Market Recommendation: We're rating Upton as a hold. He'll give back some of his value in the second half, but not enough to make this season look like anything other than a breakout.

Designated Hitter, Detroit Tigers

 Projected 2007: .282, 16 HR, $135.60
 Actual 2007: .311 AVG, 22 HR, $102.78
 Projected Rank: #59; 2007 Rank: #10

Given that his overall power numbers had been declining for three consecutive seasons, PROTRADE's system was hardly radical in projecting Sheffield for a pedestrian 2007. Nevertheless, the former Yankee is showing the world that trends sometimes reverse themselves, turning in his best season at the plate since 2003. Because of his age (38), it might be surprising to find that there's little in Sheffield's profile to suggest this is a fluke, but it's the truth. This is simply a world-class hitter enjoying a late-career surge. One last hurrah? We certainly hope not.

Market Recommendation: All indicators are pointing in the right direction for Sheff. He's a solid buy.

First Baseman, Tampa Bay Devil Rays

 Projected 2007: .258 AVG, 14 HR, $110.55
 Actual 2007: .294 AVG, 22 HR, $121.93
 Projected Rank: #34; 2007 Rank: #4

So this is what statheads were talking about back in 2002. Pena has been among the most productive hitters in the league this season, drawing walks like he always has, and even providing some of the Majors' best power to boot. Given what we know about his background -- more than 1,600 Major League at-bats of varying success -- it would be foolish to say that he's a lock to be one of the best players at his position going forward, but at the same time, I'd like to think this breakout is more gold than pyrite. Teams have been impatient with Pena for half a decade; it's about time he made them regret it.

Market Recommendation: Expect a step back, but not by much.

Second Baseman, Colorado Rockies

 Projected 2007: .278 AVG, 10 SB, $117.90
 Actual 2007: .299 AVG, 17 SB, $85.25
 Projected Rank: #65; 2007 Rank: #33

More than any other player, Matsui benefits from both a recent change in scenery and a little luck for good measure. Batting a robust .348 at home, the former Mets shortstop is enjoying what so many up-the-middle Jeff Blauser-types have before him: a career year, largely thanks to a fluky batting average, but little power or plate discipline to support it. Matsui has Denver's thin air on his side, however, and he's always been able to hit in the .270 range, even in tough ballparks like Shea Stadium, so predicting a second-half collapse would be premature.

Market Recommendation: Given Matsui's circumstances, it would seem he's a fine candidate to continue taking advantage of Coors Field, posting the highest batting average of his career. However, his second-half forecast will highly depend on his playing time.

Left Fielder, Los Angeles Dodgers

 Projected 2007: .291 AVG, 13 HR, $140.00
 Actual 2007: .375 AVG, 4 HR, $49.29
 Projected Rank: #107; 2007 Rank: #55

There was never any question that Kemp could hit. In more than 1,400 Minor League at-bats, he crushed to the tune of .309/.357/.516, and began the year as the organization's third-best overall hitter. Nevertheless, no one saw him starting quite this hot. With a .375 average under his belt, it would take a slump of pretty massive proportions to bring him down to even our start-of-the-season forecast. With a spot in the L.A. outfield finally cleared for his bat, we like Kemp for a final line approaching .315, 18 HRs, 65 RBIs and 50 runs scored.

Market Recommendation: Kemp will endure some tough stretches in the second half (remember what happened to Andre Ethier last season?), but that's emphasizing the negative. He'll also be L.A.'s best-hitting outfielder with a bullet.