clock menu more-arrow no yes mobile

Filed under:

A primer on using strike zone graphs

What is a strike really, when you think about it?

Some moderate amount of ruckus was made after Jose Bautista took a some-what controversial (according to the internet) walk off of Edinson Volquez in game five of the ALCS.

It was such a decisive call that even the home plate umpire who made the call said he got it wrong

Or...maybe he didn't

Either way it was a close call and thankfully because the internet is awesome we have several ways to remember it.

There are also other fortuitous (I think) ways of looking at it too.

We certainly don't have a lack of options here to view this. Unfortunately there are some discrepancies is the visual presentation of the data. Maybe it's not the presentation but the interpretation of the data. We objectively know where the 3-2 pitch landed: 1.5 feet above the plate, 0.5 feet to the right of it. The question comes down effectively do is that a strike or not, and that's where some confusion comes in play.

A little more than a week ago the incredibly smart and well-worded Dave Cameron wrote an article on a similar note as this article, pleading for TBS to change their strike zone chart.

But if there's been one consistent theme on a nightly basis, it's been that fans of of the Cubs, Cardinals, Mets, and/or Dodgers have felt like they were getting absolutely screwed by the home plate umpires strike zone. During nearly every game of the two NLDS series, Twitter has lit up with complaints from fans who think the zone is far too wide to both sides of the plate. Now, you might say Twitter is a platform built on getting people to give knee-jerk reactions in real-time without considering the accuracy of their comments, and I'd agree with you, but the differences in number of complaints between the zones in the ALDS and NLDS have been very obvious.

And that's because the ALDS games have been broadcast on Fox Sports 1 or MLB Network, while the NLDS games have been broadcast by TBS. And, for whatever reason, the visual box that TBS has chosen to represent the strike zone during their broadcasts is ridiculously small.

Gamecast (shown below) is a notable culprit for rousing people on the internet into arguments over ball/strike calls. The reason is that Gamecast uses the rule book definition strike zone.

Under this zone definition the final pitch to Bautista (#10 in green) was a strike for the most part, but it's not insane to think that it could have been called a ball too.

There has been a ton of research on the seemingly ever expanding strike zone that batters face now, with some suggesting that it has been the cause for the declining run environment we've seen the past 10 years or so.

A year ago Jon Roegele wrote that the strike zone expansion is out of control and then updated his findings this past August showing that theright handed zone continues to expand well past what the was the left handed zone is. Fellow smart-minded writer (to Jon and Dave; not me) wrote last September about the continued expansion downward in the strike zone.

People in the past have lamented the absence of the high strike. Baseball has responded by adding strikes somewhere else. People in the past have lamented the significance of pitch-framing technique. Baseball has responded by seemingly reducing the differences between the best and the worst pitch-framers.

So that brings us to the point of this somewhat pointless article: knowing what you are citing and what you are looking at. Not that anyone on this particular site (writers, readers, or commenters) have been cavalier in their usage of strike zone graphs. Instead use this as a primer in understand what you are looking at when you look at something or someone posts something for you to look at.

Pitch F/X

Let's start with the basics here. I'm sure you are all familiar with what Pitch F/X is, but in case you aren't here's some information from Fangraphs on what it is and isn't:

PITCHf/x is a pitch tracking system, created by Sportvision, and is installed in every MLB stadium since around 2006. This system tracks the velocity, movement, release point, spin, and pitch location for every pitch thrown in baseball, allowing pitches and pitchers to be analyzed and compared at a detailed level. Two mounted cameras in each stadium are used to track each pitch and establish the each aforementioned aspect.

What sort of separation in movement Zack Grienke does get with his pitches? Did Andy Sonnanstine change his release point at some point during the season? Which pitcher had the most break on their curveball? These are just a sample of the multiple questions you can answer using PITCHF/x data. The possibilities are nearly endless.

If you use MLB's Gameday, then you have already seen live PITCHf/x data first hand. There are many different websites and resources for PITCHf/x, including right here at FanGraphs.

Basically everything strike zone related comes from raw Pitch F/X data and then each site/provider decides how to present it from there.

Brooks Baseball

Brooks is kind of the go to for pitch F/X really (in my opinion). They were one of the first sites to really track Pitch F/X and provide so many different ways to interpret and analyze pitches, pitchers, batters, and even umpires.

There are two things to remember with Brooks: sometimes they use the rulebook zone and sometimes they use the called zone

Rulebook zone

Called zone

It can be hard to tell the difference between the two but it's there. The lower boundary of the first chart deliniates are about 1.75 feet above the plate. The lower boundary of the second chart does it at 1.5 feet above. Also on the second chart you have the grey shaded lines as well. The gray shaded lines represent what Brooks calls "typical deviations" in the called zone. Those deviations vary by handidness too.

As mentioned earlier, right handed batters typically get a bit more leeway on both inside and away compared to their left handed peers.


FanGraphs doesn't have a ton of information out there on how they classify their zone in particular but they do use the realistic/called zone. Their zone includes both the modern strike zone AND the deviations that Brooks describes above.

If you want the most realistic zone (and one that is the most liberal too) then FanGraphs is the way to go.

Baseball Savant

Baseball Savant is the newest Pitch F/X site out there but it is certainly not the smallest in possibilities as it rivals Brooks Baseball. Baseball Savant caters a bit to a different type of inquiry though. Instead of just throwing graphs and charts at you (like Brooks does), Baseball Savant lets you submit Pitch F/X queries and go from there. Want to know how Eric Hosmer hits with a runner on first and second, no outs, at home, with a left handed pitcher on the mound, at home in the ninth inning?  Baseball Savant cand find that for you (it's .333 by the way). Not only do they have excellent inquiries but great visual interpretations too.

Here's a visual look at that question/answer:

Baseball Savant has wonderful information for players on the other side of the battle in pitchers. For instance here's their strike zone graph and call from the Bautista walk above:

Baseball Savant gets their information from MLB Advanced Media but it seems like they use the called zone instead of the rule book zone (couldn't get confirmation from the site owner).

According to Baseball Savant, Blue Jays starter Marco Estrada benefited from some generous calls (even more so by the rule book definition)


Gameday is really peculiar. Since they are a direct MLB product you would think they use the rule book zone and they do as far as I can tell. However sometimes it looks like they use a bit of an expanded zone, but not necessarily the called zone.

One thing Gameday/MLB used to do was some manual plotting of the zone. During batting practice "the guys in the truck" would manually plot and configure a different strike zone for each batter based on their height so that Jose Altuve and Chris Carter don't have the same zone on Gameday. This strike zone then sticks with the batter for the remainder of the game.

The operator identifies the batters belt, then puts the top of the strike zone four inches above that point.

Baseball Heat Maps

Our own Jeff Zimmerman could probably tell you more about how his site measures the strike zone (and he's done extensive research on it). From what I can tell he doesn't use the rule book zone, but an expanded/called zone.

The question now is which one should we use/care about/look at/fight over/etc... The rules are there for a reason and an argument could certainly be made for using the rule book definition of the zone. That's what the umpires are taught, no?

However an argument can be made too that the rule book zone just simply isn't realistic. Instead we should look at pitches based on how they are being called by umpires and judge from there. Theory is only theory and we want real world applications.

Whichever argument you're for is up to you. I simply wanted to provide you with a bit more information on what the internet is probably forcing you to read.