Why Are Minor League Pitchers Walking So Many Batters?

Castillo is a bit of an oddity in that he had one of the highest walk rates in the minors despite having absolutely no power. His .042 isolated slugging percentage ranked dead last among hitters who batted 400 times. 

Holliday, Johnson and Williams are promising middle infielders and Top 100 Prospects, so the focus will be on them. 

Johnson (71%) and Williams (65%) spent a majority of their seasons in the Low-A Florida State League. The FSL uses the automated ball-strike system, which has dramatically spiked the walk rate in the league compared with pre-ABS times.

But the FSL strike zone is not the only culprit in this case, because both Johnson and Williams walked at a slightly higher rate at High-A following promotions. Holliday maintained high walk rates at all four levels of the full-season minor leagues, but the Minor League Player of the Year is such an outlier in this regard that he may not be the best basis for comparison.

As intriguing as Johnson and Williams are as prospects, it would be illogical to consider their plate skills—as well as Castillo’s—to be so elite as to become the first 100-walk teenagers in the full-season minor leagues in 27 years. 

Prior to the pandemic, the teenager with the most walks in the minors would typically have around 80. Jeisson Rosario had 87 in 2019. Jaff Decker had 85 in 2009. Miguel Sano walked 80 times in 2012. Fernando Tatis Jr. drew 75 walks in 2017. Those are four of the seven highest totals for teenagers from 2006 to 2019.

So something else must be afoot, something that would make conditions in 2023 more favorable for free passes.

As it turns out, minor league pitchers were more liberal with walks this season than they have been at any point in the modern history of the minor leagues. 

For the first time in at least the past 60 seasons, the overall minor league walk rate for the four full-season levels topped 11%, meaning that 11 out every 100 plate appearances ends with a walk. (Thank you to Dan Hirsch of Baseball-Reference.com for supplying the data.)

In fact, the global minor league walk rate has increased in each of the past seven seasons. The walk rate this season was nearly 24% higher than it was in 2019, before the pandemic, and 36% higher than it was in 2015, the calm before the coming storm of free passes.

And it’s not just younger, inexperienced pitchers at lower levels missing the strike zone. Walks were up dramatically at every level of the minor leagues. In fact, Triple-A had the highest walk rate in 2023.

You’ve seen the data. What is the context behind the inexorable uptick in walk rate?

Velocity Over Pitchability 

Stuff plays in MLB, and that preference has pushed the control artist, “thumbing” lefty and finesse pitcher to the brink of extinction. That trend trickles down to the minor leagues, where organizations prioritize and select for velocity and other pitch traits.

This trend extends to the minor leagues, where attrition rates for pitching prospects mean that it takes five or more minor leagues to produce one quality major leaguer. Thus bat-missing ability is prized above attributes like strike-throwing ability, pitch sequencing and overall savvy. 

Not only has the walk rate climbed precipitously in the minor leagues the past seven seasons, but so too have rates for hit by pitches and wild pitches, which are up 58% and 20% since 2015. Balks too are up sharply, but that is likely the result of the pitch timer.  

As velocity has climbed, precision has diminished. It’s an effective strategy against world-class MLB hitters, especially when combined with  the near-endless supply of hard-throwing relievers teams today have at their disposal in the major league bullpen and at Triple-A.   

The only thing that will reverse this trend is if MLB limits teams to 10 or 11 pitchers on a 26-man roster. That would effectively force teams to dedicate at least a few roster spots to pitchers with endurance and pitchability to avoid burning out the bullpen. 

Fewer Fastballs

More is better applies not only to fastball velocity but to breaking pitch velocity. Today, sliders are thrown harder than ever—and they’re also thrown more frequently.

The notion of a fastball serving as a primary pitch has become somewhat outdated. Fastball share has decreased at all levels of professional baseball, while other pitches—particularly sliders and changeups—have filled the void.  

This results in fewer strikes being thrown in the minor leagues as younger pitchers work through their mechanics and learn to command pitches that require more feel.  

Static Umpiring Crews

Minor league umpiring crews are a party of two for all six games of a series. One scout theorized that as the series progresses, savvy hitters are able to gain greater familiarity with each of the two umpires’ strike zones and use that to their advantage. 

A Walk Is Better Than A Hit

From the pitcher’s perspective, a walk has a lower expected run value than any hit type. Therefore, refusing to give in and issuing walks, especially to hitters capable of impacting the ball, can be an effective mitigation strategy.

ABS At Triple-A 

Triple-A pitchers walked 12% of batters this season, which is far and away the highest rate of the past 60 seasons.

The major league walk rate this season is 8.6%. 

So why are advanced minor league pitchers so much more wild than their major league cohorts? 

The answer is ABS.

The automated ball-strike system in use at Triple-A for the first time this season has a more restrictive strike zone than the major leagues. Pitches at the top of the strike zone are called balls by ABS, but human umpires in MLB have a bigger established strike zone. 

The skewed strike zone at Triple-A resulted in MLB organizations skipping pitching prospects over the level in greater numbers.

Number of 24-and-under pitchers to make at least five Triple-A starts
2018: 67
2019: 61 (introduction of MLB ball)
2021: 38 (post-pandemic MLB injuries force premature callups)
2022: 52
2023: 45 (introduction of ABS)

In Summary

While teenage hitters like Jackson Holliday, Termarr Johnson and Jett Williams have advanced plate approaches and high upsides, their walk exploits are overstated based on walk inflation in the minor leagues.

The walk rate at each full-season minor league level is 20% to 30% higher than it was in 2019, before the pandemic. 

To put this in perspective: A batter walking 20% of the time in Low-A in 2019 would have a walk rate 119% above the level average. 

A batter walking 20% of the time in Low-A this season would have a walk rate 75% above average.

The difference is even more stark when comparing players in 2023 with players in 2015. This underscores the dramatic context change in the minor leagues over the past seven seasons and serves as a reminder to not always take minor league surface performance at face value.