Everyone knows that the Braves signed Troy Glaus for his bat, not for his defense. After all, he was signed to play first base, a position that he has played a grand total of 6 games at in his career. He was not exactly a great defensive third baseman, either. Clearly, we should not expect him to play Casey Kotchman- or Mark Teixeira-level defense. What should we expect, though?
To find out, I looked for recent instances of players who moved from third base to first base. I used the 2002-2009 seasons because those are the only ones with UZR data available at FanGraphs. (For those of you who are unfamiliar with UZR, it basically measures the number of runs a player adds or subtracts with his glove compared to an average defensive player at his position.) UZR is not a perfect statistic, but it is freely available and is obviously superior to simplistic stats like fielding percentage.
I restricted my search to players who had appeared in at least 100 games at both positions during the 2002-2009 time frame. Using these criteria, I found 9 players who started at 3B and ended up at 1B. I then found the total UZR at each position for each player. To make the numbers easier to compare, I calculated each player's average UZR over a 1,000-inning period.
What did I find? Well, the 9 players, collectively, had a UZR of -2.5 for every 1,000 defensive innings at third base. Those same players had a UZR of +0.5 for every 1,000 defensive innings at first base. For some context, a good first baseman averages at least +4 UZR per 1,000 innings, and a bad one averages -4 or worse. In other words, these players were (on average) mediocre third basemen but perfectly average first basemen. Graphically speaking:
Just to be clear, this is not a *huge* difference, but given the sheer number of innings in the sample (over 50,000), it is somewhat revealing. Generally speaking, players do seem to improve their defense a small amount upon being moved from third to first.
So what about Glaus? Well, his UZRs have been erratic from year to year, but he has generally been a below-average third baseman. His UZR per 1000 defensive innings is -2.6. This is conveniently very close to the average 3rd baseman in our sample. So, based on these numbers, I would expect Glaus to be a roughly average 1st baseman in 2010.
If you are interested, I have broken down the numbers even further below. The 9 players I used in the sample are: Hank Blalock, Miguel Cabrera, Jorge Cantu, Shea Hillenbrand, Eric Hinske (another recent Braves signee... interesting), Aubrey Huff, Phil Nevin (remember him?), Chad Tracy, and Kevin Youkilis.
Only two of these players (Tracy and Youkilis) were above-average 3rd basemen--Youkilis, in fact, was excellent at the hot corner. Interestingly, these are also the only 2 players in the sample whose numbers were noticeably worse at 1st base.
The remaining 7 players all had fairly bad UZRs at 3B (ranging from -1.9/1000 innings to -11.3/1000 innings). Of these 7, 3 players (Blalock, Huff, and Nevin) were just as mediocre at 1B as they were at 3B. The other 4, however (Cabrera, Cantu, Hillenbrand, and Hinske) improved fairly dramatically. Here is a bar graph showing each player:
I also made a radar graph. It's a bit harder to read, but I like it a lot because it shows just how much improvement some of the players made after the switch. In the graph, further from the center means better defense. Blue is 3B defense and red is 1B.
So the question, to me, is this: which player is Glaus most similar to? If he is like Nevin, Huff, or Blalock, then perhaps we should not expect any improvement at all in his defense. On the other hand, if he is more like Hinske, HIllenbrand, or Cabrera, we should expect a fairly dramatic improvement. What do you think?