This is Nate Freiman’s first post as part of his August residency. Nate is a former MLB first baseman. He also played for Team Israel in the 2017 World Baseball Classic and spent time in the Atlantic and Mexican Leagues. He can be found on Twitter @natefreiman. His wife Amanda routinely beats him at golf.
Editor’s Note: a version of this work was recently presented at SaberSeminar 2018.
In 2011, I was playing at High-A for the Padres. I’d graduated from the Midwest League to Lake Elsinore in the California League. (They have the cool storm-eyes logo, but it scares my toddler so my old hats are in boxes.) Since we were so close to San Diego, we got lots of guys on MLB rehab assignments. I was a senior sign making $1,300 a month, so it was huge when someone like Orlando Hudson came through and bought us Outback.
During their assignments, every MLB guy got The Question: “What’s it like up there?” The best answer I ever heard was, “Chuck E Cheese for adults.” O-Dog, as Hudson was known, had a pretty strong reply, too: “Better balls, better lights, and a better zone.”
In this case, “better zone” means two things. The first is size. (“That’s outside!”) The second is consistency. (“That’s been a strike all day!”) And O-Dog was right: the umpiring (just like the play on the field) does get better as you go up. We’d be in some cramped clubhouse, playing cards, and eating our $11 PB+Js, watching the big club, when a pitcher would inevitably yell, “That’s a strike!” And maybe it was… by Northwest League standards.
But those standards are different than the ones at higher levels. For example: have you ever seen a check swing get overruled? I have. In Boise, back in 2009. The hitter at the plate checked his swing, and the umpire responded by yelling, “Yes he did!” After the batting team complained, however, the home-plate umpire decided to appeal to his colleague at third base, who ruled it not a swing. I’ve never seen something like that before or since.
It’s no secret that the umpiring in the majors is superior to the sort found in the minors. It’s also no secret that part of the superior umpiring is a smaller, more well defined zone. But what about the different levels of the minors? Does the strike zone get smaller at each level? Does it get more consistent? I wanted some answers.
Building the Model
In order to get them, I needed minor-league TrackMan data. That data is all proprietary, but one team sent some of it to me on the condition of anonymity. (If anyone from that organization is reading this, thank you again!) The org in question sent me a sample of 20,000 taken pitches divided across the four full-season levels. The team trimmed the data to contain only horizontal and vertical location, pitcher and batter handedness, count, and a binary “strike” or “ball” call. There was no other identifying information.
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