New Arsenal Metrics Highlight How the 2024 Brewers Succeeded by Maximizing Deception

Last week, Baseball Prospectus unveiled its latest line of pitch arsenal metrics. Unlike most models developed in recent years, which attempt to boil the various attributes of a pitch into a single stuff-based rating, these measurements try to quantify deception and the interplay between pitch types.

More specifically, these metrics are designed to study how deeper arsenals can be effective, even if they may not jump out stuff-wise. Models like Stuff+ often favor relievers, who usually throw two or three pitches at high velocity for no more than one turn through an opposing lineup. By contrast, starting pitchers must give hitters more looks to counter increased familiarity with each at-bat and work deep into games.

The complete primer is free to read here, but to summarize, the folks at Baseball Prospectus developed four metrics to measure how effectively pitchers with several pitch types create deception:

Pitch Type Probability: The probability a hitter will correctly identify a pitch before he must make a swing decision, based on release point, early trajectory, and the count in which the pitch was thrown.

Movement Spread: The size of the distribution of possible pitch shapes. In other words, how great is the variation of movement the hitter could see on any given pitch?

Velocity Spread: The same as movement spread, but for velocity.

Surprise Factor: How surprising the pitch’s movement was to the hitter based on movement spread.

Some important caveats are that deception alone does not correlate with success, nor is it a total replacement for great stuff. A pitcher with less deception but nastier pitches may enjoy better results than a pitcher with more deception but worse stuff. There is no one-size-fits-all blueprint for productive pitching. Rather, several permutations of stuff, deception, command, and sequencing can lead to positive outcomes, with the precise mix varying for each hurler.

Deception played a key role in the 2024 Brewers’ success in building a patchwork rotation amid a myriad of injuries. This site has featured plenty of coverage directly from the clubhouse about how Chris Hook and company value and maximize masking pitches, whether it entailed encouraging pitchers to throw multiple fastball variations or adding pitches to fill gaps in a pitcher’s movement spread.

It is unsurprising, then, that such a staff was filled with standout performers in these new metrics. Most of Milwaukee’s bulk pitchers had some of the least impressive stuff in baseball, but they succeeded by making it extremely challenging to identify what pitch they had thrown before hitters had to make a decision.

That’s a tower of blue in the stuff column and a sea of red throughout the rest of the table. Colin Rea, Frankie Montas, and Tobias Myers, each of whom took turns carrying the rotation for stretches, had some of the lowest pitch type probabilities in the league. Those who didn’t were soundly above average in multiple other categories. None of these guys overpowered hitters with raw stuff, but they created a challenging at-bat by making pitches look similar out of hand, giving hitters wide ranges of movement and velocity to cover, violating their expectations with a pitch’s movement, or all of the above.

These figures also further explain why the Brewers targeted pitchers like Montas and Aaron Civale as midseason additions to the rotation. Neither had inspiring numbers at the time, but both had the deceptive potential the Crew has handled well in recent seasons.

New models rarely introduce breakthrough discoveries about effective pitching. Instead, they quantify what most baseball people already knew, making those skills and strategies easier to identify, develop, and repeat. That’s the case here. Mixing speeds and locations while making everything look similar to the hitter at release has always been among the keys to working deep into games.

As these stats are refined further and more granular splits become available to the public, there will be opportunities for further analysis. For now, they present a more concrete way to recognize pitchability while shedding more light on how the 2024 Brewers kept chugging along by turning overlooked pitchers into quality innings-eaters.