Last year, the Seattle Mariners won 85 games after only 61 victories in 2008, an improvement of 24 games, the best such improvement in Major League Baseball in 2009. This year the San Diego Padres are off to an excellent start with a 17-11 record and are in second place in the National League West, just percentage points behind the San Francisco Giants. That’s an excellent uptick (so far) for the Padres after going 75-87 in 2009. One of the keys for the Mariners in 2009 was their defense, and defense is also playing a major role for the Padres this season.

In The Fielding Bible—Volume II, we developed a technique to measure defense called Defensive Runs Saved. Using a variety of methods, we estimate how many runs each player saves (or costs) his team defensively compared to an average defender at the same position. Some of the skills that are measured are range, throwing effectiveness for outfielders, ability to turn the double play and handing bunts for infielders, and effective positioning. We develop team totals by adding up all the runs saved for every defender on each team.

We estimate that the Mariners defense saved them 110 runs in 2009. That’s the best team total we’ve recorded since we began measuring Defensive Runs Saved in 2003. Comparing those 110 runs saved in 2009 to the Mariner team total of 16 in 2008, we can attribute about nine wins of their 24-win improvement to defense. This year, the Mariners have picked up right where they left off with 29 team defensive runs saved through the first month of the season. Franklin Gutierrez (seven runs saved), Jose Lopez (10), Jack Wilson (6) and Ichiro Suzuki (5) have all been stellar in the field so far.

In the National League, could the Padres be the Mariners of 2010? Few analysts predicted the Padres for a good season, but they have the third best record in the National League. Last year the Padres had the worst keystone combination in the senior circuit. Their second base and shortstop defense cost them 34 runs. This year, San Diego’s double play combination (David Eckstein and Everth Cabrera) has saved seven runs defensively thus far, a very nice improvement. The Padres center fielders (Scott Hairston and Tony Gwynn) have saved eight runs with their gloves and throwing arms. As a team, the Padres currently have the third best defense in baseball with a total of 23 defensive runs saved. Here are the top defensive teams so far:

The Los Angeles Dodgers are the antithesis of the Padres. They are in last place in the NL West and it’s their defense that’s hurting them. Their defense has cost them 17 runs thus far this year, the worst total in all of baseball (tied with the Kansas City Royals). Comparing their total to the Padres, the 40 -run difference translates into a difference of four games attributable to defense (using the 10-runs-per-win rule of thumb). The Dodgers (11-16) trail the Padres by five-and-a-half games. Defense matters.

Here are the teams struggling defensively this year:

For a complete breakdown of Team Defensive Runs Saved, visit Bill James Online at billjamesonline.com