Even as recently as 2008, the average major league hitter slashed .268/.338/.424. The average hitter in 2014 slashed .255/.318/393. Those numbers disregard pitcher at bats. The difference between the two slash lines is quite significant. Hitting is hard, but it has seemingly never been harder in the modern era than it is now.

We can attribute the decline in runs over the past decade to many different factors, but one factor may give pitchers an advantage over batters on every single pitch: the expansion of the strike zone.

The current strike zone “rule” is as follows:

Rule 2.00: 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.”

The rule is pretty straightforward. Theoretically, the strike zone shouldn’t change from one era to the next without a rule change, and yet, we are seeing the strike zone expand every season without a rule change since 1996. Jon Roegele at the Hardball Times posted this informative table in an article last October showing strike zone growth since 2008.

Courtesy of the Hardball Times

Wow. Since 2008, pitchers have gained 39 square inches of extra strike zone with which to work. The bottom of the zone seems to have expanded the most. Fangraphs recently posted an article showing the drastic increase in called strikes at the bottom of the strike zone (and slightly below) the last several years. This zone is indicated in the graphic below.


Courtesy of Fangraphs

The following list shows the percentages of called strikes within this area during the last seven years:

  • 2008: 47%
  • 2009: 47%
  • 2010: 52%
  • 2011: 56%
  • 2012: 64%
  • 2013: 70%
  • 2014: 76%

Umpires used to call this zone a strike less than half the time. They now call it a strike just over three fourths of the time. This change has led to a higher percentage of strikeouts and a smaller percentage of walks throughout the league. In 2008, the major league walk rate (BB%) was 8.9% and the strikeout rate was 17.0%. In 2014, those numbers were 7.8% and 19.9% respectively. The difference between those numbers may not seem substantial, but the large sample size is deceiving.

For another perspective, batters (without pitcher at bats) struck out 30,876 times in in 181,655 plate appearances in 2008. In 2014, batters struck out 35,421 times in 178,409 plate appearances, almost 5000 more strikeouts in about 3000 less plate appearances.

The called strikes also have another effect: hitters are swinging at more pitches that are difficult to drive because pitches at the bottom of the zone are now called strikes. These swings produce less loud contact and may contribute to the downturn in slugging percentage since 2008. Batters swing at pitches down in the zone and below about 4% more often than they did in 2008. Batters traditionally have trouble driving the ball in this part of the zone, which is why pitching coaching preach the merits of “keeping the ball down.”

What is the role of the expanding strike zone on the declining run environment? That is difficult to quantify, but some statisticians have tried. People who understand mathematics much better than me at the Hardball Times suggest that more strikes and less balls equals less runs scored, which makes sense.

They took the number of balls and strikes from the three regions where the strike zone has changed the most: the outer edge of the plate for right-handed and left-handed hitters as well as the bottom of the zone for all hitters. In our timeline from 2008 until now, we see a drastic decrease in the expected runs scored based on the number of strikes and balls called during the season in these regions.


Courtesy of the Hardball Times

Brian Mills, a professor at the University of Florida, wrote an academic paper examining the performance of umpires. He estimates that the expanded strike zone has accounted for somewhere between 24% and 41% of the decline in run environment between 2007 and 2013. Even on the lower end of the scale, that is staggering.

Strike zone expansion isn’t the only reason that run scoring has decreased in recent years, but it is one of the fixable causes. If Major League Baseball wants to increase run scoring, they should find ways to coral the strike zone overgrowth that continues to further handicap batters each season.

One issue with addressing strike zone expansion is that umpires are actually getting better at calling the strike zone by the rule. In 2008, Umpires called 81.8% of pitches in the strike zone as strikes. In 2014, they called 90.5% of pitches inside the zone as strikes. They have improved.

This improvement may coincide with the installation of QuesTec cameras. The biggest jump in called strikes in the last twenty years came between the 2002 and 2003 seasons as cameras were installed in many ballparks. To address the issue, Major League Baseball needs to adjust the strike zone itself.

And they appear to be considering just that for 2016. Umpires and players will undoubtedly need some time to adjust to new rules, and it could cause controversy early on in the transition. But the league seems determined to increase run scoring and a smaller strike zone will likely lead to more runs in the short and long term.

The strike zone has expanded and contracted (this link is fascinating) in the rule book throughout baseball’s long history. Ironically, the last change in 1996 expanded the bottom of the strike zone, the exact part of the zone that has caused the most controversy.

We can’t pinpoint the exact impact of the expanding strike zone on the declining run environment, but we can safely say that it is significant. Modern day pitchers are bigger, stronger, and better than ever. They don’t need any extra advantages to succeed. If Major League Baseball doesn’t take action to slow the growth of the strike zone, the run environment may not have hit rock bottom.

15 Responses

  1. zaglamir

    This is an excellent post. I don’t know that there is any point being made about the “declining run environment” that makes more sense to me. While I don’t doubt the math of the Floridian, I would lean toward the upper end of his spectrum. Simply put, guys like Votto have made a living by enforcing an accurate strike zone. If you suddenly make the strike zone include nearly every hitter’s weak point (low-away), you’re going to drop the hit production. It’s just such a clean answer and it maps so well alongside the decline in OPS (2008+). Great post, Mr. Carrington.

  2. Pooter

    Very interesting article! Are you in favor of altering the strike zone? Would you they go back to how it was pre-1996?

    Also, can I just say that when I played I hated the low called strike? It aggravated me so much.

    • Nick Carrington

      I think they need to move the bottom of the zone up a little bit and also call the high strike with more regularity. One of the big problems with strike zone expansion is that hitters were used to certain pitches being called balls that are now called strikes. Hard to adjust to that after years of laying off that lower pitch.

      A change in the strike zone would undoubtedly force pitchers and hitters to adjust once more but would also force pitchers to challenge hitters with more regularity. Jeremy has some nice thoughts below.

  3. tct

    This is the issue, right here. Great article, Nick.

    I’m not a conspiracy theorist, but I wonder if MLB encouraged this expansion to convince the masses that they had cleaned up PED’s? If offense and power didn’t decrease much after drug testing went into effect, some people would assume that they hadn’t really cleaned up the game.

    I don’t think they necessarily have to shrink the strike zone that much to fix it. But they need to shift it up. Pitches that are an inch or more below the knees are called strikes while pitches slightly above the waist are called balls. High heat is hard to hit, but pitches at the navel or the bottom of the ribs aren’t really high. It’s at the letters and above that is hard to catch up with, in my opinion. Get rid of the outside strike and call pitches on the inside corner strikes, which they sometimes don’t do. Shift the zone up. Make pitchers throw up in the zone more and stop giving them the outside strike.

  4. Jeremy Conley

    This is a really interesting article, and I agree it does seem like they should move the strikezone up. Some of the pitches called strikes at the bottom are unhittable, and pitches right above the belt are frequently called balls.

    I think moving the zone up a couple inches would not only get a little offense back in the game, but it would also open up different ways of pitching that could be successful, which would make the game more interesting.

  5. Ole Joe

    It seems to me MLB hitters will generally adjust to the strike zone as they understand it no matter.There have always been “low ball” hitters and “high ball” hitters. I remember a retired ballplayer doing color commentary once saying “a big strike zone will make a hitter better, because they will be more aggressive”.
    I would not want to take away a pitcher’s ability to get out good hitters if they make good pitches.

    I’ve really enjoyed this series, trying to discover why the runs per game is down. And the writers, WOW. Fun stuff.

    I hope, before it’s over, someone writes about the advancements made in the medical care for pitchers. Especially Tommy John surgery and how it affects scoring. Twice in the last week I read, fully a third of major league pitchers have had TJ reconstruction. That might mean 1/3 of all innings are pitched by players that otherwise would not be pitching at all or at least would be pitching at a lesser skill level. Plus, guys can throw harder with less regard for the career ending injury, but mostly the guys who can throw hard do get hurt and come back with all that experience and throw hard again. I think this is why it’s harder to hit major league pitching.

  6. preacherj

    This makes much more sense than ‘blaming’ the shift for lower production. I see this point very clearly. The biggest point of contention is the lack of consistency in the called strike. I’m not even talking about the difference in umpires, but the difference in the same game. I’m in favor of some sort of electronic assistance in the calling of balls and strikes. I’m not quite in favor of going to something completely automated, but perhaps a system that forces some accountability upon the umpires to make the correct calls. So much of the baseline of baseball offense statistics begin with the strike zone. The more uniform that zone is, the more accurate the measures become.

    • GeauxReds

      If you look of the percentages of strikes that are called strikes correctly by pitch fx, the accuracy of umpires has improved greatly over the past 15 yrs. The accountability you want was imposed and postseason assignments were tied to the strike zone.

    • ohiojimw

      I think some sort of “prompting” system for the ump on close pitches would be helpful. Ideally, no one but the ump would be aware of the prompt; and, the ump would still be free to call it as he (or she) saw fit.

      Such a system would also serve as a real life training device for the umps because the prompt would be indicating to the ump what a borderline strike looked like versus a near miss ball.

      I’d also like to see assistive technology deployed on the check swing. And in this case, I’d be in favor of the “computer” having the final say….

      • Mike V

        I agree with the checked swing .. Hitting a baseball is already the hardest thing in sports and to me the poor hitter catches no breaks at all on a checked swing .. I would even change that rule to allow a checked swing to be called a ball (assuming the pitch would otherwise had been out of the strike zone to begin with) up to the point that the hitter actually takes a full swing at a pitch . I’ve seen some “check swing” strike on piches where the hitter does barely more than flinch . Give the hitters a break .. These guys throw the ball 90-95 mph regularly now days

  7. GeauxReds

    I’m not gonna lie. This hurts. Glad you guys liked the idea.

  8. Dale Pearl

    I certainly believe that the expansion of the strike zone is hurting baseball in more than one way. Arbitrary strike zones based upon an individual umpire’s preference kind of makes balls and strikes a joke. If you could emulate via some type of video program a specific game with the exact same pitches thrown and change umpires I would be curious to see the number of variations. My guess would be that some umpires would call upwards of 10% more strikes than others. Major League Baseball needs to find a way to penalize umpires that sway to far in one direction or another.

    I would say that another thing that affects the strike zone as well as the number of runs being generated also has to do the the type and the number of pitchers that teams are carrying. There are as many bench players as they used to be because almost all teams carry 6 bullpen guys and some even carry 7. The backup catcher almost certainly will never come into the game so that leaves just a small group of players to be able to come in off of the bench.

  9. wvredlegs

    Another gem of an article. We can’t call them web gems, but maybe pen gems. I agree with you on moving the zone up a couple inches would be best.
    MLB seems more concerned now with the pace of the game than run production being down. If they institute some rules on just speeding up the game pace, will they have some carry over affect on offense?
    A pitch clock? Pitchers could be in a position to rush some deliveries and could possibly groove more pitches for hitters to hit. I am totally against a pitch clock.
    Implementing and/or enforcing a Johnny Gomes rule? Where a batter cannot step out of the batter’s box after EVERY pitch to re-adjust his batting gloves and helmet. The batter will have to keep a foot in the box. If umpires will enforce it, I could get behind this change. I think it is a rule now, but is never enforced.
    And there are other changes that have been mentioned to speed up the pace of the game. These changes could have an unintentional effect on run production, either up or down.

    • redmountain

      The thing is that there is a pitch clock. They just do not enforce it. Moving the strike zone up is a good idea to spice up run production and so would calling pitches that are really balls. Guys like Bruce would be better if they did not have to try and hit a pitch that is a little low and outside. .

  10. Matt

    The rule doesn’t need to be changed. Umpiring is an art and not an exact science. Umpires are not robots. The strike zone is subjective. It changes based on the situation and level of play. People don’t want to hear that, but it is the truth.
    If you want every game to last 5 hours, then have cameras and computers call balls and strikes. Pace of play and a rhythm to the game is much more important to the overall fan experience than getting every strike/ball call “right”.

    Example as food for though here:
    I am a Reds fan so I will use Johnny Cueto as my example. Cueto is pitching a perfect game through 8 2/3 innings. One more batter to have a perfect game. Full count. Cueto throws a pitch that is an inch of the plate at the knees. Are you going to call that a ball? Not me…..batter better be swinging.

    Rules don’t need to be changed. Hitters need to get better. It should be an exception that someone bats over .300, hits 30 home runs, or drives in 100 runs. It shouldn’t be the norm. If that is the type of baseball you want then all that needs to be done is stop testing for PED’s. We had that type of game a few years ago.