There are plenty of statistics available for offensive and pitching performances, but defensive evaluations have historically been rather limited. With UZR – which stands for Ultimate Zone Rating – we have a way to attach a run value to a player’s defensive abilities.
Baseball players, coaches, and fans have long understood that defense is an important part of the game. When you see an outfielder make a great catch to rob the other team of a run, it’s obvious that the defender has made a positive contribution to his team. But just how valuable was that contribution? And who are the best defenders in the league in terms of saving runs for their teams? UZR takes us closer to having clear answers to those questions.
The Concept of UZR
UZR attempts to highlight the defensive abilities of a player in a single number. Not only does this simplify defensive evaluation, but it also provides an excellent way to compare defensive contributions to offensive contributions. UZR is measured in runs, which helps to bridge the gap between how players add value on both sides of the ball.
In other words, this stat helps to compare the value of a defensive specialist with the value of a player who hits well but contributes little in the field.
Let’s look at a real-world example to better understand the concept of UZR and how it makes player evaluation easier. Andrelton Simmons has a reputation as one of the best defensive shortstops in baseball, and his 2018 season was no exception. His UZR for 2018 was 19.7, which is an elite number (more on UZR scores later). At the plate, he recorded a 5.5 wRAA, which is above average, but only modestly. Since both of these stats are measured in terms of runs, we can see that Simmons was more than three times as valuable in the field than at the plate.
For contrast, we can look at the 2018 statistics for J.D. Martinez of the Boston Red Sox. In 2018, Martinez was easily one of the best hitters in the league, batting .330 with 43 home runs. His wRAA was a staggering 59.7, the third-best mark in baseball. If you compared Martinez to Andrelton Simmons on hitting alone, there would be a massive gap in their respective values. However, Martinez had a UZR of -2.1, showing him to be a below-average fielder. By adding defense to the mix, the gap between the two is narrowed, and we are able to gain a better appreciation for what Simmons brings to his team.
Why is UZR Important?
The development of UZR was a huge step in the right direction with regard to defensive evaluation. Statistics such as fielding percentage fail to capture an accurate picture of defensive ability, since errors are so subjective and you can’t commit an error on a ball you didn’t reach in the first place (meaning players with good range could actually be punished in terms of fielding percentage). By incorporating things like range and arm strength, and by equating the value of defensive performance in terms of runs, UZR represents a notable progression in statistical analysis.
How is UZR Calculated?
There’s no way around this point – UZR is complicated to calculate. When you stop to think about the task at hand – summing up a player’s defensive performance in a single number, it’s easy to understand why the math would get quite complex. If you are interested in getting deep down into the weeds of UZR and how it works, FanGraphs has a great primer.
For now, we can provide you with four elements that are used within UZR calculations, so you can have a basic understanding of what is included:
- ARM: This is Outfield Arm Runs, and it assigns each outfielder a number of runs above or below average with regard to preventing base runners from moving up.
- RngR: Range is a big part of playing good defense, and some defenders naturally cover more ground than others. Range Runs provides a value to that coverage.
- ErrR: While fielding percentage is not particularly useful in a vacuum, errors are still a part of defensive evaluation. This stat is Error Runs, and it assigns a runs lost value to the mistakes made by a fielder.
- DPR: This last one is Double-Play Runs, and it identifies what a player has added to his team through proficiency in turning double plays.
What is a Good UZR?
Earlier, we mentioned that Andrelton Simmons had a UZR of 19.7 in 2018, which is an excellent performance. Overall, breaking 15 in UZR for a single season is going to place a player near the top of the league, and anyone over 10 is a quality defender. Obviously, those in negative territory are below average defenders, and will likely need to contribute notably with the bat to be of value to their teams.
Best UZR Seasons, 2002 – 2018
2018 UZR Leaders
What are the Problems with UZR?
There is a human element involved with UZR analysis, as people have to review each play to determine the value added. This obviously comes with a margin of error, so UZR has its limitations. Also, with how much variance there is from game to game, it’s best to look at a full season of data as a minimum, and ideally several seasons for an accurate representation of a player’s ability. That said, every stat has its drawbacks, so don’t let these minor issues prevent you from using this statistic as a piece of the overall player evaluation puzzle.