By traditional standards of measuring a pitcher’s effectiveness, Red Sox righty Daisuke Matsuzaka had a stellar 2008 season. With an 18-3 record and a shiny 2.90 ERA, one would be led to believe that he was one of the very best starters in the majors. When one digs a little deeper, however, there are plenty of trends that point to regression for Matsuzaka in 2009. Here are a few of the factors working against Dice-K:

BABIP: Matsuzaka got plenty lucky on balls put in play in 2008, with a .267 BABIP. BABIP for a pitcher tends to hover around .300, and in fact Dice-K posted a .306 BABIP in his first state-side campaign in 2007. Even if we allow for Matsuzaka to post a slightly lower-than-average BABIP because of the quality of Boston’s defense (the Red Sox posted the 5th-best Defensive Efficiency in baseball), he’s still due for regression to the mean.

Walk rate: As any Red Sox fan can attest, Matsuzaka has a maddening tendency to nibble at the corners. Dice K’s walk rate went from a mediocre 3.52/9 in 2007 to a bloated 5.05/9 in 2008. Among starters with at least 100 innings pitched, only Tom Gorzelanny, Fausto Carmona and Barry Zito walked more batters per nine innings. For the record, none of those three guys had an ERA under 5.15.

Home run rate : Matsuzaka’s home run rate fell from 1.10/9 in 2007 to 0.64/9 in 2008. However, there are no real trends to support that drop, as Dice-K generated about the same number of groundballs (about 38 percent), flyballs (43 percent) and line-drives (18 percent) in both seasons. The only difference was a dip in his home run/fly ball rate, from 10% in 2007 to 6.1% in 2008. HR/FB rates tend to normalize around 11 percent for pitchers, so Matsuzaka is due for regression to the mean here as well. As a flyball pitcher, Dice-K is pretty unlikely to give up just 12 long balls ever again.

Left on base%: Dice-K stranded 80.6% of baserunners in 2008, well above the league average and his 2007 showing (73.9%). If that number comes back to earth, so will his ERA.

All of these auspicious numbers led to a large dichotomy between Matsuzaka’s actual ERA (2.90) and his Fielding Independent ERA (4.03). That’s the third-largest difference among starters tossing at least 100 frames (Armando Galarraga is first, Justin Duchscherer is second).

None of this is to say that Daisuke Matsuzaka is a lousy pitcher. He ranked among the top 20 starters in strikeout rate and, as his Fangraphs page attests, Matsuzaka has a cornucopia of pitches at his disposal. However, if you’re expecting another sub-3 ERA from Dice-K, you’re going to be sorely disappointed. Don’t let those W-L numbers fool you: Matsuzaka is good, but not that good.