Back before the winter meetings started and there were all kinds of trades and free agent signings to analyze that took up all of our writing here, we were all ridiculously excited about the addition of UZR data the FanGraphs statistics section. Now that we have a lull in transaction analysis, I want to get back to talking about UZR, fielding metrics, and evaluating the best ways to view them. Most of my posts the rest of the week will focus on these issues.
Starting off, I want to talk about positional context. If I asked you who the best defensive player in baseball was, would your answer be Carl Crawford? Probably not. He’s definitely an asset defensively, but does anyone think he’s really the best defensive player in the game? His 2008 UZR/150 is better than everyone else, though, so if you were just sorting the entire league by that metric, Crawford stands head and shoulders above everyone else.
However, we all instinctively understand that the quality of defenders at each position is not even. Crawford rates remarkably well as a left fielder in large part due to the fact that left fielders are lousy defenders as a group. In fact, if we just look at UZR/150 for qualified left fielders in 2008, only three of the 13 players on the list have above average rankings – Crawford at 28.6, Fred Lewis at 12.1, and Matt Holliday at 5.2. The bottom of the list is populated by guys who should be DH’ing – Pat Burrell, Raul Ibanez, and Adam Dunn. Teams use left field as a hiding ground for good hitters with lousy defensive abilities in order to get their bats in the line-up, so when a team like Tampa goes the alternate direction and sticks a good glove in LF, he’s going to look like a superstar, thanks to the relative uselessness of his peers.
If Crawford played CF, which is his more natural position given his defensive abilities, he’d certainly rate a lot lower than +28 runs. This isn’t because CF is any harder to play than LF, but simply because the people he would be compared to are much better defensively than the people he’s compared to as a left fielder. This should seem somewhat obvious, but I’ve seen a lot of people talk about relative defensive rankings for up the middle players being lower because of the harder nature of the position, but it’s really just the peer group that is chosen for comparison.
If Carl Crawford was put into a room of 5’5 people, he’d appear tall. If he was put into a room of 6’5 people, he’d appear short. Think of left field, right field, first base, and designated hitter as positions of short people. You don’t have to actually be the best defensive player in the league to look like a defensive whiz when the standard you’re being held to is so low.
This is why, when you see us talking about total value of a player, you’ll see position adjustments come up in the discussion. Since each player is being rated by UZR relative to average at that position, we have to come up with a scale that neutralizes all of the averages so that they’re somewhat similar to each other.
Tom Tango has developed the most commonly accepted set of positional adjustments out there right now, based on historical data of how players perform when they move from one position to another. His scale is as follows:
Catcher: +12.5 runs
Shortstop: +7.5 runs
Second Base: +2.5 runs
Third Base: +2.5 runs
Center Field: +2.5 runs
Left Field: -7.5 runs
Right Field: -7.5 runs
First Base: -12.5 runs
Designated Hitter: -17.5 runs
Essentially, the width of the spectrum of major league players being used at their best positions is about 30 runs – if you have a league average defensive catcher and you make him a full time DH, you’ve whacked about three wins off of his value.
These positional adjustments match up with common knowledge pretty well – catchers are scarce, shortstops are the best non-catcher defenders, and the immobile stiffs get hidden at DH/1B/LF/RF, depending on how just how immobile they really are. It’s the middle part of the spectrum – second base, third base, and center field – that cause some disagreement. We’ll get into those three positions specifically this afternoon.
Dave is the Managing Editor of FanGraphs.