Midterm report: how much has Tigers' defense improved in 2015?

The Detroit Tigers finished the 2014 season with one of the worst defensive teams in the American League. As a team, they ranked among the bottom three teams in the league, depending on your choice of metrics, giving up a 105 to 110 run differential to their main division rivals, the Kansas City Royals.

The Tigers made moves to improve their defense, both in the infield and the outfield. The return of Jose Iglesias to the shortstop position, and the additions of Anthony Gose and Yoenis Cespedes in the outfield promised to give Detroit a much improved defensive team in 2014.

Here is a look at how the Tigers' 2015 defense compares after 81 games to their 2014 season, and how they stack up against other teams in the AL. First, a comparison of the defense overall, then a breakdown position-by-position.

What do these metrics mean? Click on any of the headlines above to get the definition of a given metric from Fangraphs.com or Baseball_Reference.com. There is a quick description of the metrics at the end of this article, which is well worth reading if you're not familiar with the meaning of these defensive metrics.

FanGraphs tells us that it takes two seasons of data to accurately measure the defensive efficiency of a given player. This is due to random variation in small samples of balls in play. When looking at a full team, however, there are many more plays and much less chance of luck skewing the numbers.

By almost any measure, the improvement in the Tigers' overall defense is impressive. They have gone from being one of the three worst defensive teams to one of the top four. The improvement is evident across the board.

Now, let's break down the Tigers' defense, position-by-position, starting with the overall outfield defense. This is the area where the Royals held the biggest advantage over the rest of the league in 2014.

Outfield was the weakest link in the Tigers' defense in 2014, with Torii Hunter being the worst defensive outfielder. Rajai Davis was well below average as a corner outfielder in the AL. Replacing Hunter with Cespedes and limiting the amount of time that Davis spends in a corner position has helped the outfield defense tremendously. The team has gone from 13th to fifth in overall outfield defense.

The Tigers already have more outfield assists than they had in all of 2014, and they have made more out of zone plays than any team in the league, leading the first place Royals by 20 gems. However, there is still room for improvement in their fielding percentage, which is a sign of too many errors -- including mental lapses.

Individually, Cespedes and J.D. Martinez both rank among the top seven qualifying outfielders in DRS and UZR, according to FanGraphs. Gose has chipped in with a 2 DRS, although UZR has him rated a bit below average. Davis comes up on the negative side in both metrics, although he is a bit above average when playing center field. Using him as a defensive replacement for any of the other three outfielders is something that should never happen.

Shortstop is another position where the Tigers have seen vast improvement. Jose Iglesias has provided a boost at a critical position, leading the league in defensive runs saved (DRS).

Second base is one of only two positions where Detroit was above average defensively in 2014, with Ian Kinsler leading the league in DRS. He is again leading the league in 2015, and is second to former Tiger Omar Infante in UZR, giving the Tigers a solid double play combination up the middle.

Third base was the weakest position in the infield for the Tigers in 2014, with Nick Castellanos rated dead last in many defensive metrics, including a historically low RZR. He continues to struggle with his range, but has improved in that area, as well as his overall rating at the hot corner. Castellanos does not make many throwing errors, shows good judgment, and makes plays when he can get to the ball.

Castellanos still ranks last in range, but has improved enough to bring his defense up to just below average. He has as many out of zone plays as he had in all of 2014. Beware of small samples in just half a season, but the trend is encouraging.

First base can be a critical position if it's not manned properly, and the Tigers have a huge question mark there heading into the second half of the season. Miguel Cabrera was not exactly a plus defender at the premier sack, but he was very steady. We've added a category for "scoops," provided by FanGraphs.

Catcher is the most important defensive position, but the most difficult to measure. It's easy enough to calculate a fielding percentage or a percentage of baserunners thrown out, but things like pitch framing and how well a catcher works with pitchers are more difficult to quantify. We could write an entire article on this topic alone, and Brandon wrote one on James McCann's inability to frame a pitch, but here are some numbers.

Considering the fact that the Tigers' starting catcher, Alex Avila, has missed much of the first half of the season and they have relied on rookie James McCann to handle catching duties, they have fared very well at this position. The Tigers led the league in both steals allowed and runners thrown out in 2014. Detroit catchers have not committed an error this season.

Following are some definitions for the defensive metrics used in this article. Click on the title for a complete description.

Defensive runs saved (DRS) is Bill James' fielding bible gives a measure of overall defense by a player or a team with zero being league average at a given position.

Ultimate Zone Rating (UZR) is an advanced system for measuring runs above or below average. UZR/ 150 projects the UZR over 150 games, to even out any differences in the amount of time played.

DRS, UZR, and OOZ are cumulative, so you need to double the numbers from the first half of 2015 to compare to 2014, as you would if counting home runs or errors.

Revised Zone Rating (RZR) is the percentage of balls hit into a given player's zone that are turned into outs. The zone is defined as a play that is made at least half of the time in major league baseball. The zone is standard and does not account for defensive shifting.

Out of Zone (OOZ) plays are those where a player goes out of his zone to record an out. It is also cumulative.

Defensive Efficiency Rating (DER) is the ratio of team defensive outs recorded in defensive opportunities. Divide the total number of hits allowed (except home runs) by the total number of balls in play and subtract from 1.000.

Fielding percentage is the percentage of plays that are converted to outs, divided by the number of plays made by a fielder, using the subjective opinions of the official scorer. Basically, subtract the percentage of errors from 1.000.

Rank here uses the average ranking of DRS and UZR to rank teams in the league from 1 to 15. Both metrics ranked the Tigers 13th in 2014. DRS has the Tigers second in 2015, while UZR has them fourth.