Inside the rules: the strike zone

A recent article here at The Hardball Times arguing for instant replay on balls and strikes prompted the subject choice for this installment of MLB rules analysis. The call for today’s technology, which appears capable of outperforming human eyes, is logical. Automation of the strike zone could provide consistency from game to game and batter to batter. It could also eliminate what’s often perceived as differing interpretations of the strike zone between umpires or leagues. The case for automation also holds the promise of a quicker flow to the game, inferring that a computerized strike zone would eliminate arguments from batters, pitchers, and managers.

Despite all those potential benefits, this article will attempt to argue against instant replay on balls and strikes. But first, it will relay the customary history of the rule in question.

Baseball’s earliest years saw no semblance of a strike zone as we now know it. While the width of the plate has been a constant, in the late 1800s, the batter could call for a ‘high’ or ‘low’ zone. This reduced the size of the strike zone from between the shoulder and knee to half that size according to the preference each batter voiced. In 1887, hitters lost that beneficial clause when the rule changed and the zone included the entire area from the knee to the shoulder. This remained, at least in the stated rulings, unchanged until the 1950 season. That year, the rules lowered the top of the zone and defined it as between the armpits and the knees. The zone went back up to the shoulders briefly, starting in 1963, before restoring the armpit level as the high point in 1969.

1988 saw a different type of update to the top, as the upper limit of the zone stopped at “a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants.” Finally, in 1996, baseball broke the previously established pattern of adjustments, as it left the upper limit static for once. This modification actually moved the lower level instead. The new boundary fell below the knees, to the ”hollow beneath the kneecap.”

This is the current wording of the rule:

A STRIKE is a legal pitch when so called by the umpire, which

(b) Is not stuck at, if any part of the ball passes through any part of the strike zone;…


The STRIKE ZONE is that area over home plate the upper limit of which is a horizontal line at the midpoint between the top of the shoulders and the top of the uniform pants, and the lower level is a line at the hollow beneath the kneecap. The Strike Zone shall be determined from the batter’s stance as the batter is prepared to swing at a pitched ball.

It is important to note that any part of the ball passing through any part of the three-dimensional zone constitutes a strike. This widens the strike zone from the 17-inch diameter of the plate to a width including almost the entire ball on either side, adding over five inches to the horizontal limit for the zone.

Vertically, the umpire must not only determine the defined midpoint of the player, often called ‘the letters,’ but also account for that level as the batter starts the loading phase of his swing. All that has to be done in an instant to set the upper limit of the zone. The umpire must also account for any part of the ball passing through these boundaries as well, which of course makes the lower and upper edges slightly lower and slightly higher than a line running out from those points.

The interesting part about the rulebook modifications to the strike zone throughout time is that its evolution may lay in part with the players. Over the years, pitchers generally stayed away from letter-high pitches over the plate because those often end up crushed. Umpires followed by starting to call the borderline high pitch a ball since they rarely saw one thrown there, and certainly not often thrown there on purpose. Finally, so goes this hypothesis, after pitchers, hitters, and umpires adjust over time to a lower strike zone, only then did the rulebook make it official, eventually dropping it from the shoulders to the armpits to the chest.

Such shifts in borderline calls, if truly originating with the way the players play the game and the umpire’s response to that, portray MLB’s definition as more of a guide than a rule.

Umpire equipment is another potential catalyst for a shifting zone. For a time, many umpires wore the ‘balloon’ chest protector worn on the outside of the uniform. This more bulky chest protector was prevalent in the American League, with the last one finally gone in the mid-1980s. The smaller protector, worn under the uniform, allowed more flexibility for umpires and could have led to the National League’s reputation as a ‘low strike’ league for a time as those umpires could more easily see the bottom of the zone. Conversely, the higher strike zone allegedly had a home in the American League.

Now umpires in both leagues wear the same, smaller equipment under their uniform, leading to more uniformity.

If those factors truly represented the origin story for strike zone fluctuations throughout baseball history, technology changed that.

A Hardball Times Update
Goodbye for now.

MLB started using measurement technology in 2001 to compare umpire’s calls with results tracked with several cameras in select stadiums across both leagues. The system, made by a company called QuesTec, also produced its fair share of controversy. Of course the system made umpires nervous, as MLB officials used data from the system to grade balls and strikes calls from the men in blue.

There also were complaints that the system recorded pitches inconsistently, as the system plotted the expected path of the last few feet of a pitch. Detractors felt that the system misrepresented late-breaking pitches and sometimes projected a different location than the actual location. It also angered a few pitchers, most notably Curt Schilling, who destroyed a QuesTec camera at Bank One Ballpark in 2003.

Those against the system had additional fuel in their fight against it, as the company faced severe financial difficulty, even after securing the contract for MLB.

Despite the complaints, the QuesTec era ended with many officials agreeing that the strike zone became more consistent under the system. It didn’t just help umpires in parks with the machines. Alan Schwarz reported in 2009 that the Elias Sports Bureau found a very small difference, certainly not enough to be statistically significant, in the way umpires called games in QuesTec stadiums versus games without the technology.

That success prompted MLB to switch to a new system, called Zone Evaluation, in 2009. This system uses more cameras, promising to be more accurate. It’s also used in every park.

Technology is available, and it is helping umpires call a consistent zone.

The technology also makes for interesting analysis on the internet, notably here. Tools like Pitch f/x allow people to dig deeper into balls and strikes, and the referenced article is one in a series where the author looks at pitchers that may get preference and possible differences between the zones for left-handed batters versus right-handers.

People have long suspected umpires of giving leeway on calls in the zone to certain players. Ted Williams’ eye was so renowned that legend has it that umpires called anything the great hitter let go by late in a count as a ball. On the other side, Atlanta’s talented twosome of Greg Maddux and Tom Glavine seemed to get strike calls further and further outside as games went on.

But, although Pitch f/x has shown some slight deviation from the rulebook, that deviation is somewhat consistent and doesn’t reveal a blatant disregard for the strike zone. It may simply reveal the standard accepted and even endorsed by batters and pitchers.

Those in favor of instant replay on balls and strikes may deride ‘the human element’ that differs from findings based on technology like Pitch f/x. They may very well be justified in doing so, as the human element has led to some rather famous missed calls in all sports, not just baseball. But, ridding baseball of that element is not something that just has bothered old, grouchy players stuck in the past. Although, it certainly has bothered them, as an ESPN survey showed 39 of 40 Hall of Famers opposed instant replay on balls and strikes.

Another ESPN survey, this one of current players, showed that the players are overwhelmingly opposed to instant replay on fair or foul calls. Given the lack of gray area on those, and the ease with which replay could be implemented there, it’s easy to suppose that current players would agree with the Hall of Famers and be against replay on balls and strikes by an even greater margin.

If players don’t want replay, and play under a system they agree works well with the umpire interpreting the zone, it’s hard to see why we’d want replay for any other reason than our own selfish ones.

Joe Posnanski wrote recently about the human element. Although he primarily focused on football’s instant replay, he also mentioned baseball. At one point he said this about the strike zone:

“Yes, of course, there must be dimensions, there must be rules, and they should be specific. But it strikes me that by playing with the rules we sometimes lose the intent. By messing with the specifics, we sometimes lose the overall purpose.”

Yes, the intent. One may argue that umpires can’t possibly know intent. They may argue that an umpire can’t know the intent of a pitcher on a balk call or the intent of a batter on a checked swing. But, in that regard, reels upon reels of replay film can’t either. It is a fact of baseball that umpires must judge intent of players and have the authority to make their call.

Furthermore, baseball, if taking replay all the way to balls and strikes, may fall victim to one of the few very bad things about the N.F.L. and college football. That is the utter lack of spectator joy, by anyone able to store memories lasting more than a week, on close plays. That is in spite of an immediate call on the field.

A Fumble? Who knows, really? An official makes the call, but that means nothing until we see if the red flag comes out and then sit through dozens of replays. Then we hear the ruling of the official that somehow we—even though we’ve seen the play over and over—somehow can still come away with a different opinion than the official.

And that’s the supposed gold standard of replay: the NFL.

If replay is instituted on balls and strikes, we must likely be prepared to lose, and perhaps lose often, the finality of a called third strike. A Justin Verlander curveball that once ended at-bats may just become one of several challenges in a game already criticized for lasting too long.

If we’re to be selfish in our calls for changes in the game, we should demand to cling to the spontaneity of a called strike, not demand replay on the strike zone. The human element in baseball is something that’s part of baseball’s fundamental core, not just romantics clinging to mystical lore. The very first words in baseball’s rulebook define the game:

1.01 Baseball is a game between two teams of nine players each, under direction of a manager, played on an enclosed field in accordance with these rules, under jurisdiction of one or more umpires.

Jurisdiction is the power and authority to interpret and apply the law. The very definition of the game involves an arbiter, one who must apply these rules in the manner they see best. Therefore, under the very definition of the game, arbiters judge players and apply the rules as they interpret them.

Umpires judge balks and check swings, even plays at first. Their role, a primary part of the game, is a role that includes interpretation and application of rules.

That interpretation and application applies to the strike zone as well and should remain final.

References & Resources
In addition to the links referenced within the text, Baseball Digest, The New York Times, St. Petersburg Times, The Denver Post, and The Official Rules of Baseball Illustrated all proved helpful.

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11 years ago

If there is an argument for instant replay I suppose football has it. There are so many tiny events going on in a single play that the officials can’t possibly see them all and even if they do they don’t always have the best angles. I’m not sure instant replay really improves the game but at least that’s the argument. Instant replay in baseball is ridiculous. Especially on balls and strikes, the umpire is right there with the clearest view in the house. If the players themselves don’t think its necessary or even want to consider it it leaves it to a few disgruntled fans who take things way too seriously and expect perfection where none exists. Lets not have any more delays in a game that goes on way too long already because of technology, I’m referring to the lengthy breaks between innings because of commercials. Besides, if we can’t have a good argument once in a while about whether a guy was out what fun would there be?

Lindell AC
11 years ago

The use of Ques-tec type systems can never be used in place of an umpire for ball/strike decisions for one simple reason. The definiton of a strike is not simply as you stated, part of the ball passing through a defined strike zone.

Action continues regardless of whether or not some laser scan technology lights up a red light because the ball hit the zone. In many situations runners are moving based on the umpires official signal of ball or strike. Your article didnt consider the checked swing and the appeal process involved with that situation. Did he go? Yes or no? Also, what about questions involving a dropped third strike? Did the catcher scoop the ball out of the dirt or catch it clean? Did the ball pass through the strike zone but was dropped by the catcher? What if the batter leaned into the strike zone and was hit by the pitch? (By rule still a strike).

There are way too many variables that are in effect simultaneously for a computer to give a timely definitive ball or strike call. Sure you can call timeout when the ball becomes dead, send the umpires to the video room and break it down like the Zapruder film. Then have them come out and move base runners back, cancel or add outs, change the score and reset the count, but that in itself would violate the rules.  Somewhere in the rule book there is a general clause that states that nothing can be done which could be classified as “making a travesty of the game”.

David Wade
11 years ago


My article deals with the called strike, so the zone is as simple as I defined it.  I’ve already written about the uncaught third strike, but haven’t done the check swing- which might be good to put in the queue, I suppose.

At any rate, this one was meant to argue specifically against replay on called strikes and balls, not all strike calls, though I’d be against those as well.

I agree that a computer shouldn’t call strikes, and that only umpires should.

David Wade
11 years ago

I’m also totally against a machine calling every pitch.  No smoking in bars is a good thing, but has nothing to do with the definition of the game of baseball.

Besides, don’t you remember what happened with Skynet?

David Wade
11 years ago

Good point, Wayne.  That fits with my feeling, which is growing with every installment of this series I write- umpires are the arbiters of the game, for better or for worse.

11 years ago

I love that the rulebook was cited in this article.  I think the most important idea would be what I like to call the “god” rule.  That is rule 9.01 C: “Each umpire has authority to rule on any point not specifically covered in these
rules.”  This allows the arbiter absolute control.

Paul Francis Sullivan
11 years ago

Why for better or for worse if there is a better way to do it?

I have yet to hear a logical reason why umpires should be allowed to call a strike different from batter to batter.

How is that remotely good for the game?

David Wade
11 years ago

How sure are we that each specific batter gets a different strike zone?  We probably shouldn’t use our own anectdotal evidence, as a pitch that looked right down the middle in an Oriole-Yankee game may show up well outside the zone on PitchFX.

There are a few guys using PitchFX and heatmaps and all kinds of good data mining to try and examine the strike zone empirically.  I.E. the Benefit of the Doubt series at Beyond the Box Score, along with other stuff Tango links at Inside the Book. 

While those studies have sometimes found a different zone (for Mariano Rivera, or for ALL left handers, for example), the ‘difference’ in the results in the data are not extreme, in my opinion.  Especially when the guys doing the best job collecting the data believe PitchFX can have up to 1.2 inches of measurement era.

That’s not to mention some bias in sampling say, different zones for different counts.  Perhaps the zone IS larger in a 3-0 count.  But, is that because umpires subconsciously favor the pitcher in that count?  Or is it because a pitcher doesn’t purposely work the edge of the strikezone?  In other words, you’ll usually see far fewer borderline pitches when a pitcher’s trying to avoid a walk. 

That not only makes an easier strike call for the umpire (‘bigger’ zone), but also makes the sample on borderline pitches verly likely smaller than when a pitcher is ahead in a count.

I’ve said all that to say I believe there’s not some huge difference in strike zone calls from batter to batter.  IF that’s right, then how is it bad for the game, since the game is defined by having an umpire call the balls and strikes?

Paul Francis Sullivan
11 years ago

Sorry, but I can’t disagree more. What I was suggesting was an instant call, not a replay. Basically using a fine tuned version of what was used by the TV network showing the strike zone and where it crossed or didn’t cross the plate.

I am all for the human element in baseball, but with the players and the strategy. The human element of Brooks Conrad not making the right play, or the Phillies leaving third base open allowing Johnny Damon to take third or the poor Rangers bullpen not being able to throw a strike in AT&T Park.

But if someone throws a great pitch for a strike, they shouldn’t be penalized because the hitter is Ichiro, or that he plays for the White Sox and Joe West hates Ozzie Guillen.

The example I used before was imagine if an umpire says “I don’t call balls that land an inch fair a fair ball. It has to be a foot or more. That’s my fair zone.” That umpire would be considered incompetent.

Yet we casually allow such lunacy in the strike zone. I say let’s see what happens if we take the idiocy of different strike zones for different umpires and different players and see how it works.

I remember when smoking was outlawed in bars in New York. “It’s PART of going to a bar” was the mantra. “It gives the bar character. It’s a tradition.”

Guess what? It worked and makes the bar experience so much better.

Give it a whirl. How can “getting calls right” and “rewarding players for what that DO” be a bad thing?

11 years ago

“How sure are we that each specific batter gets a different strike zone?”

We aren’t sure at all… that’s the problem!

“I’ve said all that to say I believe there’s not some huge difference in strike zone calls from batter to batter.  IF that’s right, then how is it bad for the game, since the game is defined by having an umpire call the balls and strikes?”

I don’t think there is a huge difference either.  What I’m saying is if we have the capability to make sure the is NO difference, then we should do that.  And the era of “defining the game” by having an error prone human being make slightly wrong calls should come to an end.

The home plate ump is still required for all the other required calls…  just not balls and strikes.

David Wade
11 years ago

“The home plate ump is still required for all the other required calls… “

Why is a human allowed to call ohter plays, and not strikes?  I had assumed you’d want cameras on all forces, tags at bases (especially home), catches, etc., if you want to stop any chance for human error skewing a game.

David Wade
11 years ago

Yep, Sean.  That’s what Ques Tec did well, despite any flaws it may have had.  Now, from what I understand, the umpires are not real open about how the grading system works, but technology is used somehow in their evaluation. 

One initial fear was that under the scrutingy of systems like Ques Tec and Zone Evaluator, umpires might overcompensate and grade more borderline pitches as balls and drastically shrink the zone, but that didn’t seem to happen.

l. m. gumby
11 years ago

There is an emerging problem in baseball that this article, and some of those opposed to computerized calls, don’t seem willing to acknowledge: the advent of 60 inch HDTV’s has exposed poor calls more than ever before.  I still can’t tell if Jackie Robinson stole home safely in ‘55 or not, but if it happened today we would know if the ump got the call right.  When I see my team get the crap end of a bad call (or even the benefit) I find it infuriating.  Due to current technology I now know that this is happening frequently—too frequently IMO, and it’s only going to get worse as the technology gets better.  I’m not too bothered by a few bad calls a season, but a few in one series ruins the game for me, and I’d assume the same for the average fan. 

If there’s an ever growing problem it needs to be fixed.  Sullivan thinks that the only way to do that is to automate, and if it is the only way I agree completely.  However, I tend to side with Sean and the idea that if the bad umps are fired (and let’s face it, umpiring is part innate ability, some people just aren’t good at it) many of the bad calls will go with them.

Do some people think this isn’t a problem?

11 years ago

The use of technology to track balls and strikes can be of benefit to the game in the following manner:  DO NOT allow challenges or the technology to call the pitch, rather use it as a rating tool for the umpires.  Only those umpires who score statistically well get to keep MLB jobs.

this guy
11 years ago

We have technology that is more effective than humans, yet we’re not using it. It’s not about the sport. It’s about appeasing human emotions.

8 years ago

I still think the umpire behind the plate could use some help with some type of optical measurement possible these days. Surely computerized aided optical systems could give more accurate balls and strikes “suggestions” to the entire park relayed on a centerfield display.

No human should be given “the power of God”.

We are all human, therefore fallible.

I only wish we could take some power from other people who like to play God. Like the President, judges, cops….the list goes on!