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Mound Visit: Primer on advanced fielding stats ☕


STATE COLLEGE, Pa. -- Everyone knows the Pirates' rebirth in the 2010's was fueled in part by defensive shifts.

It seems simple enough in theory: Put the defenders where a specific hitter most often hits the ball. Facing off against a pull heavy left-handed hitter? Take your third baseman and put him in between the second baseman and first baseman. Going up against Joey Gallo, noted single-avoider? Why not get wild like the Astros did last season and put four outfielders in place, and the remainder of your defenders on one side of the infield?

Countless permutations can apply. I wanted to highlight the shift to start the next chapter in my advanced stats primer because it was the simplest to understand. From here, analyzing defense with a deeper look requires some serious math. The formulas inherent in some of these advanced fielding stats are more complex than seen in my advanced hitting stats and advanced pitching stats primers.

But, we'll get through it together.  We'll dive into only the most widely used descriptors, as the field of advanced fielding stats are very much in flux. As in other installments, I’ll pick and define such statistics. I’ll even use them in a sentence in honor of the recently completed Scripps Spelling Bee.


What is it: DRS attempts to measure players by the total amount of runs their defensive abilities either saves or costs his club. As this statistic was brought into prominence by a group of individuals comprising The Fielding Bible, I'll crib the exact components of the formula -- which is somewhat proprietary -- from their website:

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In broad terms, DRS uses errors, range, double play ability and outfield arm strength as part of its formula, and computes it into runs.

In a nutshell: DRS summarizes a defender's total fielding value as an expression of runs. Players can have a negative or positive value.

Use it in a sentence: Adam Frazier leads all Pirates defenders with at least 100 innings in the field with a +6 DRS rating. Surprisingly, Starling Marte rates as a -2 defender in 2019.


What is it: UZR also applies its rating in runs, but differs slightly from DRS. Namely, it uses a credits/debits system with far fewer variables than DRS, while adding range to the equation. UZR takes data on all batted balls and assigns them four main variables judged against the MLB-wide average:

  • Outfield runs: Runs prevented by an outfielder via his arm, be it a putout at a base or at home plate
  • Double-play runs: Runs an infielder or outfielder save via a double play
  • Range runs: Runs saved by a fielder's ability to get to a ball
  • Error runs: Runs that a fielder cost his team by way of an error

Park adjustments are also taken into account with UZR, and vary each year. For example, PNC Park's run environment would vary greatly from, say, Great American Ball Park in Cincinnati. These park factors are adjusted down so that each batted ball is weighed equally.

In a nutshell: UZR is a means to express defensive ability by runs saved or cost, but differs from DRS by using fewer factors.

Use it in a sentence: Colin Moran is the worst defender on the Pirates by UZR, with a -4.9 rating. His lack of range is a huge factor in this rating.


What is it: A new challenger to the fielding title, Fielding Runs Above Average comes to us from Baseball Prospectus and while also runs-based, differs from DRS and UZR in one very distinct way.

Rather than using zone-based fielding data, FRAA attempts to answer the question: Did a defender make a play, or didn't he? Thus, this metric looks at play-by-play data for every batted ball.  Ultimately, FRAA judges a player by the number of plays he made relative to the average of his position across all of MLB. Again, did a defender make a play or not?

FRAA has been tinkered with heavily over the past few years, and now includes pitch framing data, making a catcher's contributions much more important. The formula is proprietary, however, so we cannot truly see how these components are pieced together.

In a nutshell: FRAA uses every single batted ball to judge how many runs a defender saved or lost.

Use it in a sentence: Kevin Newman is the lone Pirates fielder with a positive FRAA on the season, with a +2.9 rating.

Advanced fielding stats still very much carry a Wild West feel, as they are constantly in flux. At the end of the day, though, a play is either made or it isn't. In that light, some of these statistics can feel a bit cumbersome. Yet, when applied in the right context, they can be helpful in quantifying what we may not see clearly with our own eyes.


June 18: Crick's slider is a sight
June 17: Saving Polanco’s summer
June 14: Brault steps up
June 13: Archer’s fastball lets him down


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