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By The Numbers

How To Win Friends And Influence Hitters

by Matt Williams
Updated On: May 4, 2021, 1:13 pm ET

One of the most popular analytics for pitching is ERA estimators. You likely know some of the more well-known ones by their acronyms: FIP, xFIP, and SIERA. Each metric measures different things in order to reach a specific conclusion, but they all have one thing in common. Each measurement aims to describe what happened and then predict the future based on player skill.

This week in “By The Numbers” we are going to take a close look at an alternate ERA Estimator from RotoFanatic, "StuffERA", and directly compare the conclusions against FIP.

First off, what is FIP? Field Independent Pitching is, as you can guess, a defense-independent pitching metric that assumes that the pitcher has no control over batted balls. The assumption is that any variation away from league-average defense or batting average for balls in play (BABIP) is more often than not, luck. This is clearly not the case, but the idea that a pitcher has the most control over strikeouts, walks, and home runs do carry a ton of weight, resulting in the metric's growing success and popularity.

StuffERA, developed by Paul Mammino, takes this idea much further. The main focus is that a pitcher’s ability to influence swing decisions, whiffs, and wOBAcon, and is a skill that is based on pitch location, pitch type, and pitch count. This leaves a measurement that acts as not only a descriptive ERA estimator but a predictive version that can outperform FIP. This way you can try to identify not only if a pitcher is forcing whiffs and weak contact, but if they are locating the ball in a way that will allow their success (or failure) to continue.

Command is a major component of measuring StuffERA as well, but as an independent measurement it is slightly overrated in terms of predicting a successful pitcher. This is to say that strong command does not always correlate with strong results. A pitcher's ability to influence whiffs and weak contact is far more important.

If you want to take a closer look at the individual influence metrics that go into StuffERA, there will be a link provided throughout the article. But first, let’s take a look at a couple of standouts that have the large gap between FIP and StuffERA early this season.


The Good News: Believe In Yusei


Yusei Kikuchi - Seattle Mariners

FIP: 4.64 vs StuffERA: 3.10


The Seattle southpaw, usually known for his poor command, was a popular offseason breakout candidate due to his increased velocity. However, Kikuchi stands out in StuffERA for an interesting reason. An 11.9 percent swinging-strike rate is barely above league average, but the 29-year-old does hold a 32.2 percent O-Swing rate (chases outside of the strike zone). 

Neither of these metrics moves the needle, but the thing that makes Kikuchi special is how and where he is generating these whiffs (chart below),


Kikuchi Influence


As you can see in the chart, there is a “heat map” for whiffs designated for each pitch count. This suggests where their most effective pitch location would be to generate a swing and miss in each particular count. The goal should be to target these areas in order to generate results. Instead, Kikuchi does the opposite. The lefty is able to entice swings and misses (black dots) outside of the hot zone, making the resulting whiffs more impressive.

Kikuchi, as discussed earlier, does not grade out well with command. This is something that is going to keep the Mariners left-hander from consistently performing to lofty expectations. However, Kikuchi does have the ability to influence poor decision-making from the hitter, which is far more valuable to a fantasy manager.

FIP sees a flawed pitcher with a 4.40 ERA that should be 4.64. StuffERA sees an undervalued pitcher with an underrated skill set that should have a 3.10 ERA. This does not take into count Kikuchi’s elevated HR/FB ratio of 20.8 percent that should normalize (this where xFIP comes in: 3.90).

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Below is the leaderboard for the largest positive gap between FIP and StuffERA for pitchers as of 5/2/21:


StuffERA Plus


The Bad News: Too Good To Be True


Zach Eflin - Philadelphia Phillies

FIP: 2.52 vs StuffERA: 4.68


Zach Elfin, like Kikuchi, had a large cheering section this offseason to have a breakout season. The 27-year-old currently boasts a 3.49 ERA and 2.52 FIP over 38 2/3 innings. Eflin is carrying a career-best 20.7 percent weak contact rate, according to FanGraphs, along with a strong 35.7 percent O-Swing rate. What’s not to like?

The question is contact, specifically his in-zone (Z-Contact) contact rate of 90.1 percent. This is not an issue if you are pitching to contact, and as we mentioned above, Eflin is generating weak contact this season so far. So again, what is the issue?


Eflin Chart


The issue is that even though the right-hander is having positive results, he is locating his sinker horribly. In the chart above, the red zone (measuring wOBA) is to be avoided, not targeted. Yet, that seems to be where Eflin’s sinker feels at home this season.

High contact rates in the danger zone will eventually equal devastating results, especially with a swinging strike rate of 9.8 percent (1.8 points below MLB average). Eflin’s sinker holds a Z-Contact rate of 97.2 percent this season with a 4.1 swinging strike rate. Do not get too hung up on the swinging strikes though, as the sinker is meant to generate contact. The point to zero in on is that 97.2 percent of Eflin’s sinkers in the zone are being hit, but most are located in a high damage zone.

This “luck” does not show up in metrics such as FIP because, on the surface, all seems well. A 5.0 pVAL is terrific and all of the individual pitching metrics suggest that Eflin is doing an outstanding job. StuffERA digs through the blind spot to find what is truly happening and what is likely to happen in the future if everything remains in its current state.

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Below is the leaderboard for the largest negative gap between FIP and StuffERA for pitchers as of 5/2/21:


StuffERA Minus


Not every outcome is the desired one, however, certain outcomes are more likely if you have the ability to influence certain variables. Targeting and avoiding certain parts of the zone, while being an obvious goal, is not properly valued in many popular ERA estimators. These same influence metrics can go a long way into discovering a more accurate way to measure a hitter's plate discipline as well.

The idea that you should walk away with after this week's “By The Numbers” is that you should always think about the “why” when doing player analysis. Surface statistics are fantastic for quick discussion and comparison, but if you truly want to take a step forward and have some fun, research how results are achieved. You may find that a player you cast aside has another gear hidden from view, or that a standout performer is standing on top of a trap door.

If you would like to check out the complete tools for Whiff influence, In and Out of Zone influence, rfCommand, and StuffERA on RotoFanatic, you can find them at this link.

Matt Williams

Matt Williams is a baseball writer/analyst for NBC Sports Edge, RotoFanatic and is the author of #2021PlayerBreakdowns on Twitter. He is the host of the Turn Two Podcast & you can follow him on Twitter @MattWi77iams.