How much will the Sox improve run prevention?

Boston’s emphasis on defense this off-season has been well known. New acquisitions Marco Scutaro, Adrian Beltre and Mike Cameron all have strong reputations for their defensive abilities. Boston also went out and signed the top free agent pitcher in John Lackey.

The question many fans are wondering is just how much they will improve from last year. I decided to look at last season’s UZR numbers (courtesy of fangraphs) from their former player and new signings at each position.

At the third base position Mike Lowell and Kevin Youkilis split time and combined for -12 runs in 2009. Adrian Beltre missed significant time with injuries but still racked up 14.3 UZR, which is good for a 26 run swing.

The Sox upgraded at shortstop by singing Marco Scutaro. Scutaro posted a 0.9 UZR in ’09 and Boston’s trio of Alex Gonzalez, Nick Greene, and Julio Lugo posted exactly the same number so no net change.

Boston brought in Mike Cameron to patrol center field. Cameron’s 2009 UZR of 10 was 28 runs better than Jacoby Ellsbury. Ellsbury had a dismal year in the field according to UZR, which had him at -18.6 runs.

Ellsbury will be making to shift to left field where he will take over for Jason Bay. Ellsbury has a small sample size of innings in left although CHONE projects him to be around +6, which is where I would cautiously predict as well. This is a 19 run upgrade over Bay’s -13 UZR last year.

All told that is nearly a 74 run difference in defense alone before taking into account the addition of John Lackey to the staff. Lackey himself could keep an additional 30-40 runs off the board.

Last year the Red Sox allowed 736 runs on the year. Allowing for some regression to the mean I can see the Red Sox improving their run prevention by 80-100 runs. This would put them around the ballpark of 630-650 runs allowed next season.