The 2017 Strike Zone Mid-Season Report

Originally published on July 20, 2017; scraped from in 2018.  

Following the introduction of PITCHf/x – and especially following the umpire’s union allowing video review of their ball/strike calls – the MLB strike zone rapidly began to change its size and shape. Between 2010 and 2014, the strike zone became much taller, and somewhat narrower; this was probably one cause of the reduced offense in that period. 

After 2014, the zone has changed slightly, but there haven’t been the dramatic shifts witnessed in the few years before that. In fact, from 2015 to 2016, the zone actually shrank slightly, for the first time in the PITCHf/x era:

We can see that there were some differences between 2016 and 2015. For the first time since PITCHf/x data became widely available in 2008, the strike zone shrank slightly in 2016. Most of the change was at the bottom of the zone, which moved up for both left- and right-handed batters, while the top of the zone also moved upward slightly. The outside parts of each strike zone also shrank a little, while the inside either stayed unchanged or perhaps expanded a tiny amount. Overall, the zone shifted very slightly upward and inward in 2016, and became a little bit smaller, compared to 2015.

In the first half of 2017, the zone has again remained fairly constant. The chart below shows what umpires have called so far. In the blue areas, they almost always called a ball; in the green, almost always a strike. The red areas show the region where a pitch was roughly equally likely to be called a ball or a strike. (This is from the umpire’s viewpoint.) I’ve drawn a polygon (white) just about in the middle of the 2016 red zone, which I call the “strike zone” for 2016, and kept that constant while showing the called pitches from 2008 (before the zone began to enlarge), 2016, and the first half of 2017:

The difference from 2008 to 2016 is very obvious; not so much the difference from 2016 to 2017.

To highlight differences, here is a comparison plot (again from the umpire’s view), with differences between the two seasons shown. Regions in which a 2017 pitch was less likely to be called a strike than in 2016 are blue; areas in which a 2017 pitch was more likely to be called a strike are in red.

Basically, it looks as if the entire strike zone has shifted slightly over to the umpire’s right, without changing size significantly. The difference is quite small – less than an inch – and it may not be real. In 2017, a new pitch tracking system was put into place; instead of PITCHf/x, data are now collected by the TrackMan system. Perhaps on average, the new system is calibrated very slightly differently from the old one? 

In any case, the important point is that the strike zone hasn’t changed its size significantly since last year, so batters and pitchers haven’t had to recalibrate their expectations, which is much more important than the apparatus.

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Catcher Framing: The Mid-Season Report

Originally published on on July 18, 2017; scraped from Dec. 2018, possibly with some missing images

A catcher can add – or subtract – several wins to his team by framing pitches, catching pitches near the edge of the strike zone so the umpire is fooled into thinking a ball is a strike, or vice-versa. Catchers who are good at this can add several extra called strikes per game, and over the course of a full season, several hundred extra called strikes add up to a handful of extra wins.

Once a catcher has caught about 40-50 games – a third to a half season or so – we can get a reasonable idea of his true framing ability. I looked at the 32 catchers who have caught over 35 games this season and calculated their framing ability. Briefly, I divide the area around the strike zone into 3-inch squares, and for each catcher, I compare his ball/called strike percentage to the rest of the league. (For more detail, see here.) 

The full list, with breakdowns of framing vs. right- and left-handed batters, can be seen here. The best catcher at framing so far this season has been Tyler Flowers, by a long way. Flowers has added 3.37 extra strikes per game to his pitchers’ total. Overall, Flowers has contributed nearly 162 strikes more than a league-average catcher would have; that is roughly the equivalent of 21 runs that Flowers has added to his team through his framing alone. Since Flowers has also been an unexpectedly good hitter this season, the Braves have received excellent production from their starting catcher so far.

We can look at a chart of Flowers’ framing effects by shading the strike zone red in areas where Flowers is more likely to get a strike than average, and blue where he is less likely to get a called strike:

For both left- and right-handed batters, Flowers has excelled at getting extra strikes from the bottom right corner of the zone (“right” from the viewpoint of the umpire). At the top and left of the strike zone, he has been roughly neutral or even slightly worse than average, but he has expanded that bottom corner to a remarkable extent. 

Just to show what that looks like a little more meaningfully, here are the locations of the pitches that were “mis-called” for Flowers – pitches outside the standard strike zone (the gray polygon) that were called strikes, and those inside the zone that were called balls:

Flowers has been an excellent framing catcher for several years, so his dominance this season is not a surprise. Less expected is the worst framing catcher of 2017 (35 game or more): Jonathon Lucroy. Lucroy was an excellent framer as recently as 2014, and in 2015 and 2016, though his skills were clearly eroding, he was at least roughly league average. So far in 2017, Lucroy has been abysmal as a framer, losing about 2.27 strikes per game compared to the average framer. Lucroy’s pitchers have lost nearly 123 strikes that a league-average framer would have given them:

Lucroy has no good framing areas; he lost strikes all around the strike zone for both left- and right-handed batters. If he has any good spots, it might be the bottom right corner against right-handed batters, where at least he gained a few extra strikes, but he also lost many pitches in that area that should have been called strikes, but that he made into balls:

Rounding off the top of the framing list in 2017 are Martin Maldonado (1.84 extra strikes per game), Yasmani Grandal (1.80), Caleb Joseph (1.74), and Christian Vazquez (1.48). Here are Madonado and Grandal’s charts; both have clear strong and weak zones, in contrast to Flowers:

The bottom five are Lucroy, James McCann (losing 2.22 strikes per game), Cameron Rupp (1.94), Mike Zunino (1.39), and Salvador Perez (0.81). Here are McCann and Rupp, who are at least close to neutral at the top of the strike zone, though they lose many strikes at the bottom:

There has been some speculation that catcher framing might be losing its importance as it has become a standard measurement. With umpires being aware of catchers’ ability to steal strikes, they might be harder to fool, and with managers and coaches being aware, the skill might be so universally taught and selected for, that only good framers are left in the majors. But that doesn’t seem to be the case. The range of framing we see so far in 2017 is pretty much the same as we’ve seen in most recent years. Framing remains a genuine catcher skill that can significantly affect a team’s win/loss record at the end of the year.

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