The 2015 Strike Zone, Through July

With strikeout rates soaring and run scoring dipping to generational lows in recent seasons, word came in the offseason that the Competition Committee would be monitoring the expanding strike zone in 2015. Given the scrutiny it is receiving at the league level, I have been tracking the strike zone over the course of the season, with updates at the end of each month. At the following links you can find the updates from the end of April, May and June.

Here are the latest data at the end of July 2015:

Recent Strike Zone History
Year Strike Zone Size(sq. in) Strike Zone Size Below 21”(sq. in) K% BB% R/G
2009 435 0 18.0% 8.9% 4.61
2010 436 6 18.5% 8.5% 4.38
2011 448 11 18.6% 8.1% 4.28
2012 456 19 19.8% 8.0% 4.32
2013 459 30 19.9% 7.9% 4.17
2014 475 47 20.4% 7.6% 4.07
2015* 477 50 20.2% 7.5% 4.11

* Through the end of July.

As I noted last month, the size and shape of the strike zone in 2015 has evolved to very closely match what was called in 2014. This is to be expected, given that umpires are assessed on a nightly basis and there has been no indication from the league that umpires would be directed to call the zone any differently this season than last.

However, walk rates have continued to fall, and strikeout rates and run scoring are trending back ever so slightly in what most would consider a positive direction. An important detail to keep in mind though is how the as-yet-to-be-played, call-up-filled month of September tends to play out in MLB.

(September – Full Season) Deltas
Year K% BB% R/G
2009 0.3% 0.1% -0.11
2010 0.8% 0.0% -0.17
2011 0.8% 0.1% 0.13
2012 0.7% 0.1% -0.09
2013 0.8% 0.1% -0.12
2014 0.3% -0.4% -0.16

While walk rates have tended to hold fairly flat in September, strikeout rates have traditionally spiked in the final month of the season. Aside from an anomaly in 2011, run scoring has tended to decrease fairly dramatically too as the regular season winds to a close. Perhaps this phenomenon suggests that September call-up pitchers have been ahead of their called-up batter counterparts. Or perhaps as the season’s games become more meaningful down the stretch, managers have ridden their better arms more heavily to increase the league-wide pitching talent level. Whatever the reason, it is clear that at least in recent history, the month of September has suppressed offense relative to the rest of the season.

As another point of reference, at the end of July last season, the league strikeout rate was 20.3%, the league walk rate was 7.8%, and teams had scored on average 4.11 runs per game. So in reality, for all the talk of the incredible performances of young phenoms entering the league in 2015 and small yet visible improvements in offense, (K-BB%) is higher yet again and runs scored per game are only flat year on year, continuing the trend toward defense that has existed throughout the PITCHf/x era.

Here is a visualization of the strike zones to date in 2015, from the umpire’s perspective:


Another metric that I’ve been tracking is the seemingly widening gap between the size of the strike zone for right-handed hitters and left-handed hitters. Here are the numbers updated thorough the end of July:

Recent Statistics for (Right-handed Hitters – Left-handed Hitters)
Year Strike Zone Size (sq. in.) BB% K%
2009 6 -1.8% -0.4%
2010 5 -1.7% -0.7%
2011 5 -1.0% 0.0%
2012 7 -1.5% -0.2%
2013 5 -1.2% 0.1%
2014 17 -1.4% 1.4%
2015* 27 -1.3% 1.5%

* Through the end of July.

The jump in the relative size of the right-handed hitter zone that appeared last season has stayed present and even increased in 2015. It would appear the most significant difference that exists is on the inside edge of the plate for left-handed hitters, which is still called a ball more often than not.

As I mentioned in an earlier update, left-handed hitters have outperformed their right-handed hitting counterparts in both OBP and OPS in each of the seasons in the table. By having the platoon advantage more often and now an even smaller relative strike zone with which to contend, left-handed hitters are enjoying some built-in advantages.

Finally, at times it may be useful to have a formula to describe the strike zone. Of course we know that the zone shifts all the time, due both to expected variables like the height of the batter, but also to unexpected variables like the count and the number of outs. To keep the formula simple, it will ignore all variables other than the horizontal and vertical location of the pitch as it crosses the front of home plate, as well as the handedness of the batter.

A set of elliptical strike zone formulas that have correctly assigned 91.2% of called pitches from 2015 games as balls or strikes are:

RHH: ((px + 0.0208)^2 / 1.0556) + ((pz – 2.4792)^2 / 1.0209) <= 1

LHH: ((px + 0.1042)^2 / 1.0209) + ((pz – 2.4167)^2 / 0.9792) <= 1

In other words, pitches that satisfy that formula are strikes and those that don’t are balls. In the forumula, px is the horizontal location of the pitch and pz is the vertical location of the pitch as it crosses the front of home plate, as provided in PITCHf/x data.

References & Resources:

All statistics adapted from FanGraphs, Baseball Heat Maps PITCHf/x database and Baseball-Reference.

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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8 years ago

I’ve always heard that the lefty strike zone is bigger, especially on the outer edge…

8 years ago
Reply to  LHB

Outer edge, yes, entire zone, no.

Bryce Harper
8 years ago
Reply to  LHB

no comment.

8 years ago
Reply to  Bryce Harper

I guess I interpret the data here differently especially with regards to the differences between left handed and right handed strike zones. The conclusion that left handed hitters have a built-in advantage because their zone is called smaller is a fallacy. The zone may be called smaller, but it is far more irregular which I think any hitter would tell you is far more harmful than a larger, more standardized zone. The issue is not size, it is consistency. The right handed zone in that graph is nearly a perfect square, with the extreme corners seeing fewer strikes as you’d expect. The left handed zone, while smaller in area, is completely irregular, trending down and away, and leaves far more doubt in a hitters mind what may or may not be called a strike any given day.

The most recent example that got headlines is Bryce Harper on July 31st, the game he was ejected in extra innings for arguing balls and strikes. The strike three called on Harper that final at-bat was 15″ from the center of the plate according to Brooks Baseball, which means it was 6.5″ from the edge of the plate. That pitch was farther outside than the pitch immediately preceding it, 5″ off the plate and just 4″ higher, called a ball.

Even if we are willing to accept that the “recognized” left handed hitter strike zone extends 3″ off the outer edge of the plate, that ball would still be 3.5″ beyond that imaginary line. That’s a distance greater than the diameter of a baseball and nearly to the chalk of the right handed batters box, which had all but been erased by extra innings.

I think any left handed hitter would tell you that they are fine with a “shifted” zone, so long as that zone is called consistently. What you can’t have is umpires taking that extra 3″ and turning it into an extra 6″. There is no rationale for allowing umpires to regularly call strikes on pitches that are half a foot off the outer edge. And I say regularly, because that particular strike that led to Harper’s ejection was not even the most egregious of the day. His first at-bat in that same game saw a Matt Harvey fastball registered at 7″ off the edge of the plate called a strike.

I don’t think hitters from either side would care if the zone was wider in general, so long as it was called consistently and umps stopped giving pitchers those low strikes. It is easy to adjust in-out as long as you have a defined “line in the sand” to base your adjustments on, but having a zone that is expanding down (and in the case of LHH down and away) just isn’t acceptable. Bring on the robots, tell hitters the zone is going to be the plate plus 3″ (baseball width) on each side wide but go back to top of the knees for the low end of the zone.

8 years ago
Reply to  Bryce Harper

The data does not address strike variability for LHBs (it could be the case that the zones are more volatile for LHBs, it is just not addressed here) — it does however suggest less called strikes for LHBs. That is definitely an advantage and cannot be construed as otherwise.

8 years ago
Reply to  Bryce Harper

Also, this is a fairly ridiculous statement, no?

“I don’t think hitters from either side would care if the zone was wider in general”

Even when called consistently, covering more space is more difficult…

8 years ago
Reply to  LHB

This was true relatively recently. But apparently MLB has trained umpires to eliminate the outside “lefty strike” without correcting the inside “lefty ball”