Run prevention the name of the game

It's clear from their offseason additions that the Boston Red Sox are transitioning from a team that placed the utmost value on on-base percentage and power to one that emphasizes preventing runs rather than scoring them.

By just about any defensive metric, the 2009 Red Sox were one of the worst defensive teams in baseball. The numbers, though some question their reliability, are undeniable: The Red Sox ranked 16th in ultimate zone rating (-16.3), third-worst in defensive efficiency (.681) and dead last in opponents' batting average on balls in play (.320).

Given the departure of Manny Ramirez and the decline of David Ortiz, the Red Sox simply didn't have enough offense to overcome their defensive shortcomings. With no Mark Teixeira type on the free-agent market this offseason, the Red Sox brain trust decided to pursue a different course: upgrade pitching and defense, a course that the Tampa Bay Rays (went from 66-96 in 2007 to 97-65 in '08) and Seattle Mariners (from 61-101 in '08 to 85-77 in '09) followed in recent seasons with success.

The Red Sox surely swallowed hard in giving pitcher John Lackey a five-year, $82 million contract, but such is the rate for a top-of-the-rotation starter. But with defensive evaluations evolving, teams are placing varying values on players based in part on their assessments of their fielding. So a club looking to fill its needs with an eye toward defense may be able to find what it considers to be a bargain for a superior defender.

The Red Sox have clearly subscribed to that thought process entering 2010, making wholesale changes (signing shortstop Marco Scutaro, third baseman Adrian Beltre and outfielder Mike Cameron) that should drastically improve their run prevention.

As a result of their offseason acquisitions, the Red Sox now boast above-average defenders at third base, shortstop, second base, first base and two outfield positions. One way to measure that is with Fangraphs' ultimate zone rating, which converts a player's defensive contributions into runs saved (a positive number) or lost (a negative number) versus the average player while taking into account range, arm, double plays and errors.

Scutaro's career batting average of .265 and OPS of .721 might look unspectacular. However, there's more to his value than that. Scutaro, signed for a very affordable price of $5 million per year for just two seasons, has shown the ability to be an above-average defensive shortstop. Combine that with his league-average bat at the position, and he represents a significant upgrade for the Red Sox at a position that has been a revolving door since 2004. Scutaro has gone from a below-average defender in 2006 to 2.6 runs above average in 2007, 20.3 above in 2008, and finally 1.0 above in 2009 (at shortstop). With limited options available at the position, the Red Sox signed a shortstop with a solid combination of offense and defense to a short-term, low-money deal.

The Red Sox's outfield defense in 2009, according to UZR, was below average in two spots -- left field and center field. While Jacoby Ellsbury's defense is the subject of some debate, it doesn't fare well in UZR. Ellsbury rated -18.3/150, which ranked third-to-last in baseball for center fielders. Jason Bay's defense in left was also among the worst in baseball.

Cameron, on the other hand, combines solid but unspectacular offense with very good defense. Cameron is +6 UZR per 150 games over the last eight years, while Bay is -8 UZR/150. Shifting Ellsbury to left field while keeping Cameron in his natural position of center in theory upgrades the defense in two positions.

Perhaps most important, the Sox added arguably the best defensive third baseman in the game in Beltre. That the Sox obtained Beltre on such a short contract is icing on the cake.

Over the past four seasons, Beltre has ranked either first or second in baseball among third basemen in UZR/150 three times and ranks 14th among all major leaguers over the past three seasons. He was second in all of baseball -- among all positions -- in 2009 with +21.0 (second to only Mariners CF Franklin Gutierrez). Beltre had a poor offensive season and was injured in 2009, but he is so valuable defensively that even a small uptick in his production would make him one of the most valuable third basemen in the league. And the acquisition of Beltre shifts Kevin Youkilis permanently to first base, where he has become a strong defender with UZR marks of +10.3, +4.0 and +15.2 over the past three seasons.

Elsewhere, Dustin Pedroia (+10.6/150) ranked fourth among second basemen and J.D. Drew (+15.7) was first among right fielders in UZR.

Through a combination of returning players and offseason acquisitions, the Red Sox will field strong or elite defenders at six of the eight defensive positions, with Ellsbury's transition to left field leaving open the possibility that he develops into a real asset there -- similar to Carl Crawford in Tampa Bay, who is able to utilize his speed while his lack of arm strength is less exposed.

While the Red Sox won't boast the offensive firepower that defined the team during the last decade, they will sport a balanced offensive attack, which will be complemented by what is projected to be arguably the best run prevention unit in baseball. In addition to Lackey, the Sox already boast Josh Beckett, Jon Lester, Clay Buchholz and Daisuke Matsuzaka in one of the deepest rotations in baseball. The pitchers' ability to succeed will be enhanced by the strong defense that will be in place behind them, with no glaring defensive issues like the ones that plagued the squad in 2009.

So the Red Sox chose to upgrade this offseason by stocking up on what they saw as an undervalued asset -- defense -- without having to commit big bucks on long-term contracts.

Justin Havens is a researcher for ESPN Stats & Information.