Iglesias, Middlebrooks,and the Impact of Good Defense.

The Red Sox have two players almost certainly starting at the AAA level who have excited scouts and prospect writers and who may impact the 2012 season. The system’s top prospect in John Mayo’s MLB top 100, Will Middlebrooks is a third basemen who raked through two minor league levels last season while playing good defense at third base. Shortstop prospect Jose Iglesias didn’t rake by any conventional interpretation of that term, but his glove alone has kept him in the top 10 of Red Sox prospects. At just 21 years old, he could be a long term answer at shortstop and put an end to the revolving door at that position.

As soon as 2013, the left side of the Boston infield could be an impactful and home grown duo. Much of the high expectations for these players is coming from their potential impact in the field. If the experts are right, an infield of Middlebrooks, Iglesias, Pedroia and Gonzalez could be the best in the game. That is certainly an exciting prospect for a team that with significant concerns about the back-end of its rotation.

So, what impact can we expect from a plus fielding third baseman like Middlebrooks or an elite fielding shortstop like Iglesias?

The standard caveats concerning defensive production apply. To keep things in the context of runs, we need to rely on a defensive system like UZR or Total Zone and these systems are all short of perfect. Flawed as they are, they can still give us an idea what their gloves will mean, and -as is especially important in the case of Iglesias- they can help us to understand just how much their glove can compensate for less than stellar production at the plate.

Will Middlebrooks is an exciting young player. He hits for plus power, has great athletic ability and good strike zone coverage with his swing. He is routinely praise for his glove work and scouts peg him to be a plus fielder. Assuming that they are correct, his strong glove will help propel him from a slightly above average player to a real star.

Looking at third baseman over the past five years, I found 42 players with over 1000 innings at the position. I separated those players into 5 categories using a composite of Defensive Runs Saved, Total Zone with Location Data, Fielding Runs save and Ultimate Zone Rating. Classifying third baseman as elite, plus, average, weak and poor, I found averages for each skill range. With Middlebrooks projected to be a plus defender, I would expect him to save his team approximately 8 to 9 runs above average with his glove each season. With Kevin Youkilis’ declining ability, Middlebrooks could be adding closer to 12 runs above the current fielding production the Red Sox are getting at third.

That defense will help to mitigate the difference in Middlebrooks and Youkilis’ hitting abilities. Youk is still pretty elite at the plate, his 125 wRC+ was the third best mark in the AL at the position. It would be foolish to expect Middlebrooks to show that level of production in his first season or two. With his glove, if he can hit around league average, he should still manage to be a 2-2.5 fWAR player. While that does not measure up to Youk’s 3.7 mark, it is still substantial third base production. If Youk needs to transition into the DH role next season, playing Middlebrooks shouldn’t hurt the club too much. When the youngster does figure major league pitching, he could be a 4-5 win player.

Surprisingly the numbers for elite shortstops are not much different than those of the best defensive third baseman. This is because all of these defensive metrics are based on the average performance at the position, shortstops make many more plays than third basemen, but they are expected to make those extra plays as well. Jose Iglesias is an even more highly rated defender than Middlebrooks, grading at 80 for his defense scout’s 20-80 scale. Few people doubt that he will be among the top two or three defenders at the position as a major leaguer.

For my elite shortstops group, I found that they were generally able to save around 12.29 runs per season at the position. This is important for Iglesias, since he will struggle to be an average hitter at the major league level. Last season, Marco Scutaro played average defense and hit 10% better than the league average with average base running. This gave him 2.9 fWAR on the season. With Scutaro gone, a replacement of Mike Aviles and Nick Punto will likely be worth 1.5-2 wins. It’s worth asking if Iglesias could play that elite defense right now, how well would he need to hit to outperform an Aviles/Punto combination?

An interesting comparison case is Alcides Escobar of the Kansas City Royals. Escobar was elite with his glove. Fangraphs credit him with 10.2 runs saved on defense. His bat was awful though, with just a .282 wOBA for a wRC+ of 73. Despite hitting almost 30% worse than the league and being an average base runner, Escobar was still worth 2.2 wins, close to what we might get from the Aviles/Punto combo. If Iglesias’ glove is all that it has been made out to be he could be an upgrade at shortstop if he can manage to hit 15% worse than the league. At AAA last year, he wasn’t able to come anywhere near that, with just a 54 wRC+ last season. He is still just 21 though, and if he shows an improved approach at the plate this year, he could be a plus player next season and possibly even impact the team this year as a part of a platoon plan.

Neither player can really hope to match the current level of production the Red Sox are getting this season or the next. However, their gloves give them a cushion of value that will help the team as their bats develop. For a team that had few struggles hitting the ball, the added help on defense might be more impactful than the numbers suggest. If either Middlebrooks or Iglesias does impact the team this season, the impact of their gloves will probably be the reason.