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Devin Williams
Evaluating pitcher performance has been one of the longstanding challenges for MLB teams and fans alike, but a new statistic that is gaining notoriety might shed some light on how the Brewers are doing it.
Most traditional pitching statistics are based on outcomes: Hits and runs allowed, strikeouts and walks, wins and losses. While a pitcher’s skills almost certainly play some role in determining those outcomes, a variety of other factors also come into play. The quality of a pitcher’s defense, the ballpark he’s playing in and its conditions on a given day, the quality or various traits of his opponent and random chance all also play a role in determining the outcome of any given pitch or ball in play.
Traditional statistics are an important narrative tool in that they tell us what happened, but they don’t always have much predictive value for the future. There’s a divide between the question of “Has this pitcher been successful?” and “Is this pitcher good?”
Pitchers in Control
Baseball researchers have tried various methods across decades to separate pitcher skill from outlying factors to improve player evaluation. One of the early methods was Fielding Independent Pitching (FIP), first presented by Voros McCracken in the early 2000’s. McCracken argued that pitchers were in control of three things: Throwing strikes, generating enough deception to get strikeouts and avoiding solid contact. His system generated an estimated earned run average for pitchers based on walks, strikeouts and home runs and disregarding all other outcomes, which were subject to outlying factors. FIP is still commonly used today, although FanGraphs has since also distilled the luck factor a step further to create Expected FIP or xFIP.
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Even FIP and the statistics derived from it are still measuring the pitcher’s outputs, however, as a proxy for his inputs. In recent years teams have put much more emphasis on eliminating the batter from the equation entirely and evaluating pitchers based on the perceived quality of their arsenal, and public-facing metrics are catching up. Last week Eno Sarris of The Athletic published an extensive piece on Stuff+, a single catch-all metric designed to evaluate pitchers based on pitch speed, spin and movement.
The Brewers have a robust research and development team and, as such, their player evaluation is almost certainly based on proprietary metrics and data more so than the publicly-available alternatives. One unnamed MLB source told Sarris, however, that “given how similarly teams build these metrics and how similar Stuff+ is to what these teams have, Stuff+ helps the casual observer understand what teams are seeing in pitchers.”
Some of the Brewers’ more interesting offseason personnel decisions would suggest that they’re seeing something comparable to what Stuff+ is showing in their internal metrics:
- One of the Brewers’ more surprising decisions of the offseason was declining a $5.5 million club option on starting pitcher Colin Rea, who had logged nearly 300 roughly league-average innings across a pair of seasons in Milwaukee and appeared likely to add much-needed depth to the starting rotation. Stuff+ graded Rea’s arsenal at just a 94 (where 100 is average), however, ranking 21st among 25 Brewers pitchers who worked at least ten innings in 2024. Rea eventually signed a one-year contract with the Cubs.
- Similarly, across two seasons in Milwaukee Bryse Wilson had a 3.42 ERA across 87 outings as a starter and reliever, and in 2023 the Milwaukee chapter of the BBWAA selected him for the Brewers’ “Unsung Hero” award. Wilson ranked 18th among Brewers pitchers with a 96 Stuff+ in 2024, however, and at the end of the season the Brewers removed him from the 40-man roster and allowed him to become a minor league free agent. He’s since signed with the White Sox.
- Meanwhile, according to Stuff+ the best arsenal on the 2024 Brewers belonged to Trevor Megill (122), with the metric especially favoring his knuckle curve (136). That might have made it easier for the Brewers to trade Devin Williams (who had a 115 Stuff+ in his own right), one of the game’s best closers.
- Finally, former Pirates and Rockies reliever Nick Mears posted ugly numbers after joining the Brewers in July, allowing ten earned runs in just 12 1/3 innings across 13 appearances. Mears was arbitration-eligible for the first time this offseason and seemed likely to be a candidate to be let go, but the Brewers spent just under a million dollars to keep him. Stuff+ scored Mears’ arsenal during his first Milwaukee tenure at 119, second only to Megill on the team.
Teams are always searching for a new edge, and it’s possible some of their analytics departments have already developed the next new measure that will eventually render Stuff+ obsolete. In the meantime, however, the evidence we’re seeing this offseason suggests that the Brewers’ internal numbers and the public-facing metrics are pointing in the same direction.
