PCL to MLB Hitter Adjustment

by
June 30, 2023

Recently, I had to write up Luis Matos and saw he raked in AAA to the tune of .398/.435/.685 in 116 PA. Luis played for the Sacramento River Cats. in the Pacific Coast League (PCL). So far in the PCL, the league-wide OPS of .839 OPS while it is only a .728 OPS in the majors. The league-wide difference can’t be used because not all the hitters get promoted and many who do are only up for a short time. I just ran a quick test to have an idea of how much of a production drop should be expected from AAA to the majors.

To find the adjustment, compared the rate stats for all the hitters with at least one plate appearance in the PCL and the majors. Then I did this nerdy stuff:

  1. Found the harmonic mean between the two plate appearance totals
  2. Weighed the rate stat (e.g. AVG) difference by the new plate appearance mean.
  3. Summed up the weighted differences.
  4. Divide the summed differences by the summed adjusted plate appearances.

When done, I ended up with:

How Much Difference Playing in the PCL Inflates a Hitter’s Stats
Stat AVG OBP SLG OPS ISO PA
Weighted Change .080 .107 .158 .266 .078 4965

Just looking back at Matos, his 1.120 OPS in the PCL would be equivalent to a .854 OPS in the majors. Also, his .287 ISO would be the equivalent of a .209 ISO. The adjustments are rather significant and point to the high run scoring environment of the PCL.

A couple of notes on the adjustments.

  1. The adjustment might be on the light side. Some hitters are coming back from injuries and need to play in some rehab games. They may not be 100% to start the rehab assignment but in better shape once they get promoted.
  2. Besides many batted balls falling for base hits, the walk rate is up in AAA because of the automated strike zone (first blurb).

With every hitter being called up from the PCL looking like they are going to set the world on fire, I provided a little perspective on how their production is expected to drop.

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Jeff, one of the authors of the fantasy baseball guide,The Process, writes for RotoGraphs, The Hardball Times, Rotowire, Baseball America, and BaseballHQ. He has been nominated for two SABR Analytics Research Award for Contemporary Analysis and won it in 2013 in tandem with Bill Petti. He has won four FSWA Awards including on for his Mining the News series. He's won Tout Wars three times, LABR twice, and got his first NFBC Main Event win in 2021. Follow him on Twitter @jeffwzimmerman.

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Another Old GuyMember since 2020
2 years ago

I love this article. You did make me research what a harmonic mean is. Very useful information that I actually was wondering about last night. I would be curious at some point on how to adjust pitcher stats from the offensive minded PCL.

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