What no one who has seen baseball in the last decade questions is Beltre's ability to field his position at an elite level. What has a few Red Sox fans concerned, however, is his hitting. It is not an unfounded concern, either, given his .265/.304/.379 batting line in 2009.
I, for one, am not concerned, and believe much of Beltre's struggles can be attributed to the ballpark.
Safeco, as known by many a fan, is death to right-handed hitters. As evidenced, for example, in this piece from last month on Lookout Landing, anyone whose power is to left field or center field is going to see their hitting statistics become depressed. Beltre has provided a perfect case study of the Safeco effect.
Before signing his big-money contract with Seattle five years ago, Beltre had a season for the ages. He hit .334 with a .388 OBP and a .629 SLG, along with 48 home runs, 104 runs scored, 121 RBI, and an absolute sensational season with the glove (+22.6 UZR). Long story short, it was possibly the best season of the 00's by a man not named Barry Bonds. Joining the Mariners at just 25, Beltre looked to have all the makings of a superstar.
Things never were the same for Beltre in Seattle, though. While he continued to flash gigantic amounts of leather, his hitting took a plunge, to a tune of .266/.317/.442, good for just a 101 OPS+. Fangraphs is even harder on Beltre, listing him as essentially an average hitter during his time with Seattle (-3.4 wRAA over 3059 PA). How much of this was due to Beltre, though, and how much can be argued to the "Safeco effect"?
Isolating his home and road statistics during his time in Seattle yields you these slash stat lines:
.277/.326/.472 on the road, .254/.307/.410 at home.
Given that all three of these events are proportions, it become easy to do a proportions calculation on all three (as well as ISO, or SLG minus AVG) to see if there was a significant gap in the splits. After doing the math, we are left with the results found on this spreadsheet.
I could not find a significant difference in average or on-base percentage. This is not too much of a surprise and can be attributed to bad luck on balls in play. Slugging and isolated power, however, show big differences, and they are very much in the rejection region (the region where proportion one does not equal proportion two).
Given the standard deviation, it appears that Safeco negatively affected Beltre's slugging percentage (with 95 percent confidence) by as much as .0977 points, and at least .0243 points. That is about 30-40 bases of production lost over the course of a season to a simply neutral ballpark.
Moving to Fenway, on the other hand, will be great for Beltre. Given that his power is to left field, the monster should definitely help his production at the dish, especially for extra-base hits. He only recorded 35 of them in 2009, his lowest total since the half-season he had in 1998 as a rookie.
While we will likely never see the 2004 version of Adrian Beltre over the course of the season in Boston, he will likely provide the same type of offensive production as Mike Lowell (their CHONE projections, as a matter of fact, are almost identical).
The difference is, and no disrespect to Lowell, who has had a fine career, the Red Sox go from a statue at third base with an average bat to a Gold Glove-caliber third baseman with an average bat.
This $10 million deal with a second-year player option at $5 million is a great contract for both the team and player. I just hope Red Sox Nation enjoys seeing Beltre play third as much as I will.