FORT MYERS, Fla. — According to the John Dewan Stat of the Week, the Red Sox are expected to make the biggest defensive improvement in baseball in 2010. According to the analysis of Dewan, whose Plus/Minus Ratings to measure a player’s defensive performance have become one of the most widely used defensive metrics, the Sox will go from a team whose porous defense was 52 runs below average in 2009 to one whose offseason transformation projects to result in a defense that is 35 runs better than average.

While the Sox’ defense would still not place in the projected top five in the majors by Dewan’s projections, the team’s defensive improvement of 87 runs would be the largest of any of the 30 clubs in the majors. That projection reflects the offseason acquisitions of Marco Scutaro, Mike Cameron and Adrian Beltre, as well as the move from center to left by Jacoby Ellsbury.

For those trying to make sense of the murky universe that is defensive statistics, John Dewan represents one of the oracles of the field. Dewan is the owner of Baseball Informational Solutions and co-publisher of ACTA Sports. This week, his typically fascinating Stat of the Week attempts to measure the Red Sox’ defensive improvement this offseason.

Dewan, who pioneered the plus/minus rating system (which measures how a player stacks up defensively in terms of numbers of plays made and runs allowed compared to an average player at his position), takes a detailed look at the Sox’ 2009 performance at third base, shortstop and in center field, and compares it to the performances of newcomers Adrian Beltre, Marco Scutaro and Mike Cameron at those positions. Those changes, coupled with the move of Jacoby Ellsbury from center (where he rated as below average) to left field (where he has been above average, and replaces Jason Bay, who rated as below average at the position), will have a significant effect on the Sox.

To wit, Dewan claims that the Sox will be roughly 80-90 runs better defensively in 2010 than they were in 2009. Defensively, the team was about 52 runs worse than the average team in 2009; in 2010, the team now projects to be well above average.

Certainly, that was part of the thinking for the overhaul by the Sox, who now feature former Gold Glove winners at three of the four infield positions, another Gold Glove outfielder in Mike Cameron, and two above-average corner outfielders in J.D. Drew and Jacoby Ellsbury.

“If you look at our runs allowed the last three, four years, the outlier year was 2007, and I don’t think it’s a coincidence we won the World Series that year,” GM Theo Epstein said at the press conference introducing Adrian Beltre last week. “I think we’ve been able to change the nature of our defense fundamentally, by having several moving parts. We should have a very solid infield defense, I hope, and a very solid outfield defense, and I hope that you look up this time next year and there are pitchers who are having career years, and maybe that’s a reason why.”

For a more detailed explanation of Dewan’s forecasted improvement for the Sox defense, click here.