Understanding Defensive Runs Saved, Ultimate Zone Rating, and Outs Above Average
Our articles will frequently reference non-traditional baseball statistics when discussing the performance of our beloved Atlanta Braves.
These stats get thrown around a lot and are not always explained. Does “defensive runs saved” mean a player saved that exact amount of runs with his defense? No. Does a lower DRS mean a player is worse than another? Not necessarily.
In order to ensure you are following along, we created a resource guide for commonly used stats, so you can put a face to the name.
What are Defensive Runs Saved, Ultimate Zone Rating, and Outs Above Average?
What does “defensive runs saved” mean?
Defensive runs saved is a metric that attempts to decide how many runs better or worse a player is than the average Major Leaguer at his position. So, for example, if a player has three defensive runs saved at centerfield, that doesn’t mean he’s only saved three runs, it means he’s three runs better than the average MLB centerfielder.
Three runs better is actually really good when you consider that Major-League caliber centerfielders are some of the best defensive players in the universe.
Why do great center fielders have fewer defensive runs saved than some left fielders
Some positions like shortstop and centerfield have the best athletes and defensive players, so the distance between the top player and the MLB average is not as big of a gap at other positions like right field.
How are defensive Runs saved calculated?
Defensive runs saved are calculated by the Fielding Bible. They use Baseball Info Solutions and analyze every play. If a player makes a play that only 10% of players at his position make, then he gets credit for 0.9.
That would be one minus the expectation that the play will be made for the total credit. a 10% probability is worth .9 points since or 9 times out of 10 that play would not be made. This play was way above average at the position.
They factor in everything from first basemen’s abilities scooping bad throws, routine plays, exceptional plays, distance covered, etc… If a player makes all the plays that are made 99% of the time, then they are worth very small amounts of positive points.
What creates separation is the ability to consistently make the low probability plays.
If you would like to delve into the depths of the Fielding Bible’s calculations, you can do so here.
MLB.com has a nice explanation of the stat in its glossary.
DRS uses Baseball Info Solutions data to chart where each ball is hit. Say, for instance, a center fielder sprints to make a nice catch on a fly ball. Then, say data from BIS tells us that similar fly balls get caught 60 percent of the time. That center fielder gains, essentially, 0.4 bonus points for difficulty.
MLB.com Glossary
If he can’t make the play, he loses 0.6 points. At the end of the day, that player’s overall score gets adjusted to the league average — and then that score gets adjusted for how many runs the once-adjusted score is worth.
What is Ultimate Zone Rating?
UZR or Ultimate Zone Rating is calculated and used by Fangraphs and is very similar to defensive runs saved. It takes into account factors such as range, arm strength, and errors made.
UZR compares the number of plays made by a player to the expected number of plays made at their position, factoring in the batted ball type, location, and velocity.
According to Fangraphs, UZR is defined as follows:
UZR (ultimate zone rating): The number of runs above or below average a fielder is in both range runs, outfield arm runs, double play runs, and error runs combined.
Fangraphs Glossary
Fangraphs “Def” Stat Takes Positional Adjustments out of Runs Saved
Fangraphs came up with a nifty stat called “Def” that shows a fielding runs above average and takes the positional adjustment out of the equation. We’ll use former Braves shortstop Dansby Swanson as an example.
Dansby Swanson had a fabulous 2022 campaign for the Atlanta Braves. He was great with the bat and with the glove. According to Fangraphs, Dansby had a +9 defensive runs saved at shortstop.
Again, this means he was worth nine runs saved more than the average major-league shortstop. Being an average major-league shortstop is actually really good, so being worth nine runs saved better than average is excellent!
Fangraphs has come up with a stat called “Def” that shows you how many runs better Dansby was than the average defensive player, regardless of position.
| 2022 | DRS | Def |
| Dansby Swanson | 9 | 21.5 |
In 2022, 15 of the top 20 players in Def scores were either SS, C, or CF, these are some of the most demanding defensive positions. Def is a great tool to compare those players to an average player in the league instead of just at their position, like DRS and UZR.
We’ll contrast Dansby’s numbers with the overall leader in defensive runs saved. Dansby only finished with 9 defensive runs saved and Ke’Bryan Hayes finished with 24.
Does this mean Ke’Bryan Hayes was better than Dansby on the defensive side? No. Dansby finished with a higher “Def” score than Hayes. Hayes was an excellent defensive player but the bar was much lower at third base than at shortstop. Hayes was just that much better than the average third-baseman, which is a lot worse than the average shortstop.
What are Outs Above Average (OAA)?
Baseball Savant uses a statistic called outs above average or OAA. This statistic strictly looks at a player’s success based on catch probability. This statistic is a portion of the formulas used in UZR and DRS but doesn’t include other factors.
OAA categorizes opportunities to catch a ball by the probability of other players at the position making the catch based on the distance to the ball, the time it takes to land, and the direction the ball is hit.
If a player misses a ball with a 99% catch probability then they get a -.99 from their OAA total. If they catch a ball with a 99% catch probability, they get .01 added to the OAA total. Does this sound familiar?
Outs Above Average has much of the same concepts used in UZR and DRS except it solely focuses on a player’s ability to get to a ball. Below is MLB.com’s official explanation of Outs Above Average.
Catch Probability expresses the likelihood for a ball to be caught by an outfielder based on opportunity time, distance needed, and direction. “Opportunity time” starts when the ball is released by the pitcher, and “distance needed” is the shortest distance needed to make the catch. Learn more about how direction is accounted for here. Read more about the details of how Catch Probability works here.
MLB Statcast Catch Probability Page
Outs Above Average (OAA) is the cumulative effect of all individual Catch Probability plays a fielder has been credited or debited with, making it a range-based metric of fielding skill that accounts for the number of plays made and the difficulty of them. For example, a fielder who catches a 25% Catch Probability play gets +.75; one who fails to make the play gets -.25. Read more about how Outs Above Average works here.
