About a month ago on an episode of Effectively Wild, Ben Lindbergh noted that the ability to draw walks as a minor league player has diminishing value as that player gets promoted to the major league level because pitchers have much better strike-throwing ability.

However, with the growing focus on prioritizing “stuff” in recent years, I wondered if the gap in walk rate (BB%) between the AAA and MLB levels may have started to shrink over time.

Hitters included in the sample were limited to the following criteria

• Made MLB debut between the start of 2022 and the end of 2024 seasons (years I could scrape MLB and MiLB data from Baseball Savant)

• Only included stints with a minimum of 100 PA

• Looking at the BB% differential between each hitter’s first MLB stint (that meets 100 PA), and the final AAA stint during the same season or before it

 On average, hitters in the sample lost 3.94 points of BB% when making the jump from AAA to MLB. The distribution of BB% differentials is shown here (139 hitters).

When answering the original question, of whether we have seen the gap reduced over time, the trend does not play out like I thought it might. Differentials were allocated to the MLB season for each hitter (ex. Joey Ortiz’s MLB stint was 2024, AAA stint 2023, therefore he is part of the 2024 grouping)

• 2022: -3.13 (n = 22)

• 2023: -4.11 (n = 55)

• 2024: -4.09 (n = 62)
  

In an ideal world, we have larger sample sizes per season. I would also like to include more years than just 2022-2024, and may look to do so in the future.