The Strike Zone Expansion is Out of Control

Borderline pitches such as this one are increasingly being called strikes. (via Adam Baker)

Borderline pitches such as this one are increasingly being called strikes. (via Adam Baker)

The playoffs are here, which means games are scrutinized more than at any other time in the season, with millions of extra eyeballs watching and every game crucial to the outcome of such short series. One of the most controversial aspects of each game is without a doubt the called strike zone, with seemingly no game passing without at least one team, if not both, unhappy with the performance of the home plate umpire.

We know by now that the strike zone has been expanding during the PITCHf/x era. I discovered this for the first time in the middle of last season, then followed up with a much more detailed examination of the topic at the end of 2013. Brian Mills was concurrently, independently discovering the same phenomenon, which he published in a wonderful academic paper earlier this year. All of these results concluded with data from the end of the 2013 season. Jeff Sullivan recently found evidence that the strike zone was continuing to grow in 2014, and I wanted to return to the same approach that I had used earlier to analyze the most recent regular season.

My approach involves splitting up the front plane of home plate into a 1” by 1” grid, and calculating the percentage of called pitches that crossed the plate in each grid cell that were deemed strikes. Every cell location that is called a strike more often than a ball is included in the strike zone for a given season.

What I found was perhaps not surprising – the strike zone did continue to expand, and that expansion was almost entirely due to the bottom of the zone dropping once again. What surprised me was that this season saw the largest single year increase in the size of the strike zone in the PITCHf/x era.

Average Size of Called Strike Zone (sq. in.)
Year Size
2008 436
2009 435
2010 436
2011 448
2012 456
2013 459
2014 475

The average strike zone size increased by 16 square inches in 2014 over 2013, growing the zone to a robust 40 square inches larger than just five seasons prior. In the previous articles we discussed how the zone has actually been squeezing in at the sides slightly, but is stretching like crazy down from the knees as if it is under the clutches of gravity. (And like Radiohead said in Fake Plastic Trees, gravity always wins.) I’ve zoomed in on the lower band of the strike zone by considering only those pitches that arrive at home plate less than 21” above the ground.

Average Size of Called Strike Zone Below 21″ (sq. in.)
Year Size
2008 0
2009 0
2010 6
2011 11
2012 19
2013 30
2014 47

It is clear from this table that the falling bottom of the strike zone is accounting for the entire growth of the zone as a whole. While tables show the hard numbers, looking at the strike zone visually can perhaps give a better impression of which areas are most affected and by how much the zone has changed in merely a five year span.

LHH_2009_2014_w_title
RHH_2009_2014_w_title
Note: The strike zone images are shown from the umpire’s perspective.

The box in the images is shown purely for a frame of reference. We can see that the strike zone has had a full three inches – the diameter of a baseball – tacked on to the bottom within half a decade. The called zone was wider than it was tall in 2009, but with the trimming of the sides and the massive expansion at the bottom, its width and height have become virtually equal in 2014.

Another interesting note is that while the zone for right-handed hitters has always been slightly larger than for left-handed hitters, the gap has grown to the point where righties faced a zone 17 square inches larger in 2014, on average, than their lefty counterparts. While the zone for left-handed hitters has increased 35 square inches since 2009, partly offset by a noticeable trimming off of the outside “lefty strike”, the zone for right-handed hitters has swelled an incredible 46 square inches over the same period.

Previously I’ve shown that pitchers have been throwing to this expanding band at the bottom of the zone more and more each season to take advantage of the new pitcher-friendly area, and in turn hitters are now swinging more at pitches in this region. This is a trend that continued in 2014.

Percentage of Total Pitches Thrown Between 18” and 24” Off the Ground
Year Percentage of Pitches
2008 16.9%
2009 16.8%
2010 17.4%
2011 17.3%
2012 18.1%
2013 18.2%
2014 18.3%
Percentage of Pitches For Which Batter Swings Between 18” and 24” Off the Ground
Year Percentage of Pitches
2008 45.6%
2009 45.0%
2010 45.4%
2011 46.9%
2012 47.5%
2013 48.3%
2014 49.2%

In my article examining this topic at the end of last season, I had calculated that the changing called strike zone had being responsible for about one third (31%) of the lower run environment in 2013 as compared to 2008. Brian Mills used a different technique in his analysis and arrived at a range of 24% to 41% of the earned run difference between 2007 and 2013 was due to differences in the called strike zone. Certainly with the zone having expanded again in 2014, with the largest single year increase during that period, no less, the run environment would have been expected to drop in the past season.

I updated the calculations for this past season using the same technique as I used before, which involves using wOBA constants to calculate the expected run difference by count for the next pitch being a strike as well as the next pitch being a ball and summing up these tiny run differences over all instances of called pitches to the regions where the strike zone has been changing most notably. The three regions of interest that I defined are off the outside edge of the plate for both left-handed and right-handed batters, as well as the bottom of the zone for all hitters.

Results of called pitches in three regions of interest, by year
Year # of Balls # of Called Strikes Expected Runs
2008 91,727 37,866 2,606
2013 85,556 42,456 1,892
2014 81,946 43,653 1,489

It is worthwhile noting that these numbers don’t exist in a vacuum, as we can see the total number of called pitches in these regions also declined by almost 2,500 between 2013 and 2014. The reason for the lower number of called pitches is two-fold. Pitchers have been throwing less pitches to the outside edge regions as these areas have been less likely to result in called strikes, and less total pitches has led to less called pitches. In the bottom of the zone, we’ve seen that pitch totals are getting higher, but so are batter swing rates. These swings climbed faster than the extra pitches thrown to the bottom of the zone in 2014, causing a slight reduction in called pitches in this region as well.
That being said, yet again we see the number of expected runs decline, this time by 403 runs in a single year. As a frame of reference, if we subtract this number of runs from the league total in 2013, the average number of runs scored per team per game would have dropped from 4.17 to 4.08. Teams scored an average of 4.07 runs per game in 2014, the lowest total in not only the PITCHf/x era but since 1981.

Someone inside the game recently asked me if I thought the league knew how much of an impact on the run environment the changing strike zone has made. I find it hard to believe that nobody knows, but maybe that is actually the case. It’s an interesting question – what do you think?

Retroactive Review: Ace
Looking back at some of Justin Verlander's most interesting moments.

If you like low scoring pitching duels, you probably love this type of change to the strike zone. The sentiment that I get though is that most people would prefer more offense in the game. The simple way to do that would be to simply tighten the strike zone’s belt and pull its bottom back up toward where it was when the PITCHf/x era began just a few years ago.

How low will it go? Has the zone bottomed out? We’ll have to wait until 2015 to find out.

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Jon Roegele is a baseball analyst and writer for The Hardball Times. He was nominated for a SABR Analytics Conference Research Award in 2014 and 2015. Follow him on Twitter @MLBPlayerAnalys.
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asdf
Guest
asdf

The zone expansion can be attributable to rather new types of pitches such as cut fastball, two seamer, etc. or maybe pitchers nowdays can have their balls tail more than ever. Therefore, umpires are inclined to think “This ball looked like it was hooking in when it was passing over the home plate.” or “Recently, Pitches have got more movements that I should take that into account.”
Uh, pitch framing skill is also a probable answer to this phenomenon.

evo34
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evo34

Right, because no one was framing pitched until 5 years ago..

T Byrd
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T Byrd

If a catcher is framing a pitch, it’s a ball

Joshua Northey
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Joshua Northey

T Byrd, that is totally false. Framing strikes is just as important as balls.

Mr Punch
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Mr Punch
Agree with asdf. basically, but I think there’s another factor: umps tend to give a pitcher his “out pitch,” which is not the same as being misled by it. The “new” strike zone looks a lot like Mel Stottlemyre’s strike zone in the ’60s and ’70s. Stottlemyre threw a sinker, and opponents were driven crazy because he continually got strike calls on low pitchers; umps would say “that’s his pitch.” Well, now it’s everybody’s pitch’ As for framing, I’ll say it again – it’s actually cheating, because it’s playing the umpires, and (like many forms of cheating in baseball) should… Read more »
munchtime
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munchtime
Mr Punch, it’s pretty clear you don’t understand what “pitch framing” actually is. In the words of Jonathan Lucroy… “The problem with calling it framing seems to be that people associate the term with “college crap” like trying to bring the ball back into the strike zone. If you remove that idea from the equation, ‘receiving’ is very simple according to the Brewers’ catcher: “I try to catch a ball and stop it. I don’t try to make a ball look like a strike, I try to catch the ball and stop it the best I can and give the… Read more »
matt w
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matt w
I don’t think Lucroy’s comments should really be taken at face value. He’s not going to say “Of course part of my job is trying to get pitches that are really balls to be called strikes,” because that shows up the umps and is probably counterproductive. And yet he surely benefits from that. As a Pirates fan I know Russell Martin says similar things and yet will sometimes frame pitches off the plate to look like strikes. And I don’t think this is cheating (I don’t even consider it on the level of selling a trapped fly ball, which most… Read more »
matt w
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matt w

Specifically see the Grantland interview with Martin about pitch framing:
http://grantland.com/the-triangle/qa-russell-martin-on-the-art-of-pitch-framing/

He talks about getting strikes rather than stealing strikes, partly because getting a reputation as a “strike stealer” is counterproductive. But he also says “But if you catch the ball the right way, every once in a while you do get a call.” And the interview is showing him a bunch of pitches outside the strike zone that he got called strikes.

ander
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ander

The clarity and magnitude of the zone change has to suggest a conscious decision made by umps/baseball, not an introduction of new pitches or pitch framing.

Steven
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Steven

Dear Jon, great analysis. I’d like to introduce you though to Less’s good buddy Few.

James Wetmore
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James Wetmore

Good point. I was going to mention this, but didn’t want to sound like the grammar police. I’m 59 and I was taught the difference in school. I wonder if it’s still being taught.

Tony Cunningham
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Tony Cunningham

I teach philosophy in a university, and very few of my students ever had formal grammar of any kind in school. Some folks associate “less” with the singular (“less strength”) and “fewer” with the plural (“fewer muscles”), but the most accurate way to think of the rule is that “fewer” goes with “countable” nouns (things that can be counted individually).

John Walsh
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John Walsh
Nice analysis. It looks to me like the umpires are trying to call the strike zone more by the rule book. You did not show the rule book zone in your plots, but if you did, we’d see that in 2009 the called zone was too wide and too small top-to-bottom. The general trend in recent years is to squeeze the zone horizontally and stretch it vertically. The low strike is being called closer to the rulebook now than it was several years ago. When you calculated the change in run scoring due the the low strike, did you also… Read more »
Jon Roegele
Guest

Thanks for the comment John. I referenced your work when I first looked at this topic at this level after the end of last season.

Yes, the expected run table includes the changes in balls/called strikes in all three regions that I noted were changing most notably. The outer edges for both left-handed and right-handed hitters have been contracting, so the deltas in these two regions drive expected runs higher. That shows just how much faster the zone has been expanding at the bottom, which is driving the negative expected run trend.

MGL
Guest
MGL
That is what came to my mind too. I think umpires are being “graded” or at least are getting feedback on their calls based on the “de facto” strike zone (NOT the rule book zone, which would imply a much higher zone). As John said, I think that umpires are more and more calling strikes within the zone they are supposed to call strikes in, because of evaluation and feedback. I doubt it has much to do with framing or pitch repertoire. If MLB want to reverse the trend, they need to change the zone that the umpires are graded… Read more »
Joshua Northey
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Joshua Northey

Exactly this is all about the umpires actually doing what they are supposed to with better training/feedback methods.

MGL
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MGL

Excellent article by the way! Very clearly written.

Jon Roegele
Guest

Thank you. Yes I believe the vast majority of the increase in size must be coming via feedback from MLB, since we know that umpires are evaluated on a regular basis. Brian Mills showed in his paper that I linked to within the article that umpires are getting more consistent during the PITCHf/x era. MLB must want to have the zone called in this manner. Catcher framing would be a smaller part of this puzzle I would believe.

Chaz
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Chaz

To what extent are the new, lower strikes actually correctly being called strikes? That is, are umpires conforming to what pitch/fx defines as the correct zone, and thus calling more low strikes correctly, or are they incorrectly calling low balls strikes?

Big Daddy V
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Big Daddy V

This is not all that easy to answer, as the biggest flaw with pfx is that it doesn’t always set the top and bottom of the zone correctly for each batter.

Enad
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Enad

The zone expansion IS attributable to virtually every umpire having HIS zone, which can change with the pitcher, the hitter, or the inning – which is why, with the technology available today, MLB should get rid of umpires calling balls and strikes and use machines and a truly standardized strike zone. That would speed up games, get rid of spurious “gentlemen’s strikes” on 3-0, an eliminate any bias that occurs because of the game’s situation, the inning, home crowds, etc.

KD
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KD

Amen. If the goal is to get the calls right, then let’s take out the human element. Seeing Matt Kemp get called looking on a pitch that was called a ball on the previous pitch the other night sent me through the roof. I’m sick of umpires and ” their strike zone.” There should only be THE strike zone.

Joe
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Joe
While I’m personally in the camp calling for robots (or, more realistically, a strike/ball display in the home plate ump’s mask; he’s going to be there to make other calls anyway so you might as well make him be the puppet at the end of the computer’s string). However, we should be careful not to over-exaggerate the degree to which umps are inconsistent with the zone and with each other (or themselves, on other days in other parks). Baseball Savant’s data suggest that — with a couple of exceptions — the umpires don’t actually have a zone that changes “with… Read more »
Will
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Will
Great article, Jon. The comments have been all around illuminating as well. I’d love to see a comprehensive review of all strikes, swinging and called, that tracks the decline of the check-swing ball. Anyone watching the games this season could tell there’s been a huge clampdown on check swings, and umpires have been calling more strikes than ever, and without the hesitation we’d seen in past years. I wonder to what degree the check-swing calls, coupled with a larger strike zone, have encouraged players to swing more freely. After all, there’s no point laying off a close pitch or trying… Read more »
Andrew Pautz
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Andrew Pautz
I definitely believe the strike zone expansion is a result of MLB feedback to the umpires and greater conformity to the FX strike zone. Even with the evolution of the zone the past few years, you’ll see some definite patterns in the data: FX will have many more pitches in the strike zone at the bottom of the zone than MLB umpires will call strikes (more pronounced on pitches with greater vertical movement). The top of the strike zone will also show more FX pitches in-zone than are called strikes. Finally, the outside corner will have more called strikes than… Read more »
PK Krubs
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PK Krubs
I am an ex collegiate catcher, I give catching and hitting instruction to kids, and am still very much a student of the game. My foundation in skill & especially knowledge of the game comes from big league coaches and big league players (many of the pitchers). Looking over this in depth analysis without really diving into it, I realized that % of pitch type is not accounted for in this analysis. The sinker, in my opinion, is the cause for the “strike zone expanding”. This pitch, along with the 2-seam fastball, has exploded in popularity over the last 10… Read more »
PK Krubs
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PK Krubs

“extra dimension, it makes it that much harder for a pitcher to track…” — This should be batter, not pitcher.

Jon Roegele
Guest
Thanks for the comment. You’re right that pitch type does affect the strike zone. If you click on the link for “The Living Strike Zone” article that I wrote, you can see how pitch type affects its size, and also see images at the bottom. Overall, I don’t believe that any increase in these pitch types is playing a big part in this zone expansion. Same with catcher framing. I can believe they could contribute to the issue, but I believe the overwhelming reason is because umpires are being graded daily against some desired zone by MLB, and this must… Read more »
WDavis
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WDavis
Good article. Can you explain your axes? 1. You claim a grid of 1-inch by 1-inch but there are 6 tick marks/boxes between, for example 1.5 and 2.0 on the vertical axis. Same with the horizontal. What do 1.5 and 2.0 represent? 2. Same issue, the table shows 0 strikes below 21 inches in 2009 but the plot shows a lot of strikes below 2.1 Not a big deal but I’d also recommend less use of “extreme” qualifiers. Change in “merely 5 years”, an “incredible 46 sq in”. We only have data back to 2008, we have no idea what… Read more »
Jon Roegele
Guest

Thanks. The axes are in feet. 21 inches is 1.75 feet, so includes the first three rows north of the bottom of the box that is in the image for a frame of reference.

Joshua Northey
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Joshua Northey

I agree on the overuse of modifiers. It makes things like this needlessly inflammatory and normative when there is despite the lack of evidence for such language. I suppose it probably garners more hot internet clicks though…

evo34
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evo34

Nope. It’s just acknowledging a clear trend using samples of hundreds of thousands of pitches (each year). I certainly appreciate the effort of the author in uncovering this. You can continue to believe it’s random variance; it won’t change the very real effect the change is having on baseball.

Luke Kim
Guest

We need to have computers uniformly call the strike zone. They would not show this variance that mere humans have.

Scott Lindholm
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Scott Lindholm

Excellent work. Using data from Daren Willman’s baseballsavant.com I’m convinced PITCH f/x has caused a change in how umpires interpret the strike zone.

Tom Jefferson
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Tom Jefferson

I find it interesting that batters and pitchers (at least those left in the playoffs) are saying that they respect the umpires for calling a consistent strike zone, although it requires both batters and pitchers to find out what that strike zone is for a given umpire, as the game progresses. Is there any way of documenting this?

RShack
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RShack

Just because it’s different doesn’t mean it’s out of control. It might be getting more under control.

The referent should not be the calls of previous seasons. The referent should be conformity with the rule book’s strike zone.

Jon Roegele
Guest
Thanks for the comment. The problem with trying to compare with the “rulebook” strike zone is being able to define what that is, for each hitter, mathematically. Mike Fast has a height-dependent strike zone formula, and I’ve generated an elliptical strike zone formula. But both of these are (a) relying on published height data which is sometimes “rounded up” shall we say by players, and (b) we use the umpire ball/strike call to help derive and test these formulas. PITCHf/x data has top and bottom strike zone values input by a stringer, but Mike Fast has shown these to not… Read more »
hoya33
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hoya33
Ask Jordan Zimmerman about a bigger strike zone in 2014 playoffs that ump squeezed him so bad in the 9th he could have walked up and handed the ball to his catcher in the middle of home plate and it would have been called a ball. All this stuff based on one reason the homeplate umpiring this year has been awful older umps cant figure the change from a 97mph fastball to the same pitcher throwing a 81mph changeup their old eyes cant refocus and younger umps just don’t know the strikezone.Also throw in the fact that during the season… Read more »
Ray
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Ray

The strike zone might be growing but if umpires called strikes as the zone is described in the rules the game would speed up which is what MLB wants.

Drew
Guest

Jon Miller just mentioned this article during the Giants radio broadcast of Game Three.

Livefree
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Livefree
It has become bizarre that pitches that can be clobbered with reasonable effort are called balls, and pitches that are almost impossible to square up are called strikes. Specifically, balls at the “letters” can, and often are, hit hard, yet many players are trained to see them as balls, and so they take them. The pitches below the knees have already been discussed. Why the game wants those to be strikes is a mystery. Bring the entire strike zone up, batters will get their eyes retrained, and we’ll have more offense as batters will swing more often at pitches they… Read more »
GreenMountainBoy
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GreenMountainBoy
Umpires are now getting feedback on their ball-strike calls. They’ve obviously been told they’re missing too many low (and also high – see this year’s playoffs) pitches, so they’ve adjusted. Really, they DO want to do a good job. And they’re no longer giving pitches 6″ off the outside corner, which used to drive me bonkers. See Gregg, Eric. Finally, will someone please explain to me WHY umpires HAVE to line up over the catcher’s inside shoulder??? There’s no way they can accurately call the borderline outside corner pitch from there, although, in their defense, if you see enough pitches… Read more »
Rich
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Rich
Umpires are trained to set up between the catcher and the batter, in “the slot”. If you set up right, you can se the outside corner. The reason for setting up in the slot is safety. Straight over the plate, directly above the catcher is a danger zone for foul balls. The slot is the safest place. Also, umpires are trained to track the ball all the way to the catcher’s mitt before evaluating and calling the pitch, so, “framing” or more appropriately, “sticking” the pitch will get a strike call, where as a catcher that moves the mitt after… Read more »
Jon
Guest
Jon

I have to believe that MLB has made a conscious effort to “prove” that the steroid era is over, and to do so they have initiated this effort to make pitches that are difficult or almost impossible to hit be called strikes. I agree that a strike should be a pitch that is in the “striking zone” of the hitter.

The observation that batters tend to universally stand at the back of the batters box could be a factor. Moving up in the box could negate some of this.

Jim Richards
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Jim Richards

I think it’s great that the umpires are finally calling strikes the way they should…this should end the period of on-base-percentage baseball where players go up to the plate first with the intention of driving up the the starting pitcher’s pitch count…if the Pitch F/x is lighting up when the ball crossed the knee, then that ball should be called a strike…hitters need to go up there swinging and not working the count as much as they do.

Burke Hansen
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Burke Hansen

If the square is the rule book zone, it appears that they are calling pitches more correctly. What is the point of this article?

dprat
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dprat

Is reading comprehension a declining skill or is it my imagination? “The box in the images is shown purely for a frame of reference.”

Further, “the point” seems pretty clear. Cliff Notes version: an expanding called strike zone, almost entirely in or near the low portion of the zone, apparent the last several seasons, accelerated at an even faster pace this season. This expansion of the zone likely accounts for a substantial portion of the lower run environment we are seeing.

Really, not that hard, is it?

mike
Guest
mike
What a TERRIBLE idea it is to have machines replace umpires. It’s true that the strike zone lost its upper half about twenty years ago basically by arbitrary fiat, perhaps that is the issue to be addressed. But every time a borderline strike is called on a hometown fan favorite, everyone comes out of the woodwork to call for the elimination of the umpire. It’s not bad enough that replay is the slippery slope in getting rid of human arbiters, now some want machines to do that work. Let’s take it to its logical extreme: just have a bunch of… Read more »
Harry Freiberg
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Harry Freiberg

I argue that the strike zone has NOT enlarged, but HAS moved. Based on TV provided observation the current vertical zone seems to be from just below the knee to the hips. A waist high pitch is a high strike. I can’t remember when I last saw a letters high pitch called a strike.

The horizontal strike zone seems to vary from umpire to umpire, sometimes from right-handed batter to left-handed batter. Pitches on the black are deemed a wide strike zone.

Yeah, I’m a crabby old guy whose baseball memories go back over 50 years…

mjay
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mjay
Interesting article.. Stimulating comments especially those regarding “framing the pitch”.. One aspect of framing I did not see was catchers try to frame a pitch especially the low outside corner pitch back to where it crossed the plate before they reached to catch it.. Another aspect of ump calling is catchers even more than ever set up on the edges giving the Umps better views of the plate and to see the pitchers pitches movement of the ball to see where it crosses the plate………… I like the strike zones they are the way the rules say they should be… Read more »
Bob Plezia
Guest
Bob Plezia

There has much been written about MLB SO’s going up and BA’s going down over recent yrs.

I think this analysis is incomplete until it shows how the expanded zone affected those stats!

Can you show how many SO’s had at least one strike called that was out of the strike zone/yr?

A related stat, it has been written about 30% of MLB swings are at out of the strike zone.
How many strikes or % of strikes are taken in MLB/season?

Bob

Bob Plezia
Guest
Bob Plezia

The study is incomplete because it doesn’t show the effect of the calls outside the strike zone!
How many SO’s/yr, in the last few yrs included at least one call strike of a pitch that was out of the strike zone?
And how many pitches that were strikes that were taken, by yr, and by plate app (PA)?

Bob

brad
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brad

Strike zones are inaccurate because they are called by humans partially blocked by a catcher.

Jim Murphy
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Jim Murphy
I am a former baseball fan who has abandoned baseball because it is just too boring (fans reading books in their seat, for example). Yes, tighten up the strike zone as it has gotten just too big but this is only a very small step that will not help a lot. To make this game have more action thus forcing fans to NOT take their eyes off the field for long periods of time the following changes must be done or baseball is doomed as it will continue to lose fans: 1. Reduce the effect of the pitcher – no… Read more »
George
Guest
George

The strike zone, pitchers throwing harder, and defensive shifts are all account for the declining production. The strike zone should be fixed, IMO, because it’s something that should remain constant. Let the hitters adjust to the other 2 things.

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