Is the Strike Zone Bigger in August?

Jeff Zimmerman over at Fangraphs had an interesting post about the expansion of the strikezone as the season goes on. He mentions that there may be evidence to bolster David Ortiz's claim that umpires are calling more strikes and less balls as the season goes on.

I wanted to see this for myself using my own method, so I created a called strike probability model for April 2008 vs. August 2008, April 2009 vs. August 2009, and April 2010 vs. August 2010. What I did was I pulled all called strikes and balls (ignoring all the times when the batter swings) within half a foot from the rule book strikezone, half a foot inside and half a foot outside. I then modeled a surface fit for all called strikes over pitches where the batter didn't swing. I assumed that the middle of the inner 0.5 foot border returned called strikes 100% of the time if the model did not project that far inward, and same with balls way outside the strikezone.

Let's take a look at called strikes in April 2008 vs. August 2008 to see if umpires called more strikes as the season went on in the past, where red indicates called strikes and blue indicates balls (blue balls, snicker). Note that I split the strikezone into nine equal-sized boxes for reference, while the outer border is the approximate rule book strikezone:



It looks like here that the left-right distance is not affected much, but you can see that the upper areas as well as the lower areas show more called strikes in August, if only slightly bulging. Let's take a look at April 2009 vs. August 2009:



Here, it actually looks like April had a higher probability of called strikes in the lower part of the strikezone. There isn't that much change in 2009 though compared to 2008. Now let's compare this year's April vs. the current month of August:



Is Ortiz on to something? At first, I wasn't so sure. Using the grid as reference, you can notice the red extend upwards slightly and downwards a bit more, but it didn't see like much of a difference to me. I'd have to show the numbers to back it up, as the difference in the images produced didn't seem significant enough to me. In the end, the numbers over at Zimmerman's post may well back Ortiz's claims, showing an increase in called strikes per non-swinging pitches increasing from 51.0% in April this year to 53.5% this month of August. That difference of 2.5% could very well be captured by that red dip you see in the lower third quadrants.

How much does this affect each individual batter? There were 55,240 total called strikes and balls in April. Assuming the month of August would have a similar number, that's 1381 balls converted to called strikes, 2.5% of 55,240. A quick query tells me that there were 21,191 total atbats in April, which would mean that approximately 6.5% of all at-bats in the month of August had one more called strike than in April.

Crude calculations there, but it looks like that David Ortiz might be right and that the umpires have expanded the strikezone as a whole, if only a little bit. Probably means that Ortiz had an atbat among the 6.5% of unfortunate souls who were disadvantaged by one less call in favor of the batter.

Ryan Howard's Whiffs by Pitch Type

I submitted my Mark Reynolds post yesterday to Fangraphs' community blog... and they accepted! Needless to say, I'm getting some site traffic from Fangraphs now, and I thought I'd share some plots of the other prodigious power hitter who strikes out a ton. Let's take a look at Ryan Howard, Mark Reynolds' left-handed counterpart, only 40 pounds heavier.

Ryan Howard has been either second or third in the entire MLB in swinging strike percentage and other strikeout categories since Mark Reynolds' debut in 2007. Fangraphs' stats tell us that Howard has swung and missed on 14.6% of pitches so far in 2010 while posting a swinging strike percentage consistently above 15% in the previous three seasons. Like Reynolds, Howard doesn't actually swing at everything compared to other swing-happy batters, swinging at less than 50% of pitches every season for his career.

Again, I'm going to leave out cutters and just look at four-seam fastballs, sliders, curveballs, and changeups due to sample size. Let's look at four-seam fastballs (987 pitches from RHP, 649 pitches from LHP):



It seems like Howard lets off the high fastball more than Reynolds does (or makes more contact), keeping his whiff rate below 30% against fastballs while Reynolds reached the 40% range. But just as Reynolds falls victim to low and inside fastballs from right-handed pitchers occasionally, Howard whiffs at low and inside fastballs from left-handed pitchers. Take another look at Reynolds' four-seam fastball whiff plots and notice the symmetry based on handedness compared to Howard's.

Here's a look at Howard against sliders (892 from RHP, 817 from LHP):



Looking at Reynolds' whiff rates against sliders, there's that symmetry again, but for both batters, it seems as if the opposite handed pitcher is more successful at getting either batter to whiff on sliders, which suggests that one way a pitcher can counter an opposite-handed batter's platoon advantage is to throw low and inside sliders. Of course, that's based on a sample size of the two most whiff-prone hitters in the MLB, so take that suggestion with a grain of salt.

Let's look at Howard against curveballs (675 from RHP, 518 from LHP):



These look similar to that of Reynolds, except that Howard swings and misses on curveballs more from LHP while Reynolds whiffs on curveballs from RHP, again, because of the opposite handedness.

Finally, and this is good, let's see if Ryan Howard falls victim to changeups the same way that Mark Reynolds does (982 from RHP, 274 from LHP):



Now this is telling (I'll eventually find and use another adjective to describe my amazement at a discovery). Howard swings and misses at over 30% of changeups in nearly all parts within the strikezone while he is particularly weak against low changeups from left-handed hitters at over 40% whiff rate, just like Reynolds' weakness against RHP changeups.

Maybe it's just coincidence that two power hitters with the highest whiff rates, one right-handed and the other left-handed, are weakest against same-handed changeups all over the strikezone but particularly low around the knees. Either way, it's definitely interesting to realize the main weaknesses of Reynolds and Howard. I'd imagine that knowing where to throw a certain pitch and being able to combine them effectively will get Reynolds and/or Howard to continue whiffing at a high rate. I'd also imagine that the difference between a deceptively low and inside slider and a hanging one is minuscule, even for a major league pitcher, just as a high fastball out of the zone could just as easily go down the middle of the plate. Of course, those are the types of pitches that both Reynolds and Howard can and routinely do crush out of the ballpark. To confirm that, we'll have to look at slugging percentage by pitch type another time.

Mark Reynolds' Whiffs by Pitch Type

Mark Reynolds is perhaps one of the more interesting power hitters heading into his prime this season. He has led the entire league in strikeouts since 2008, holding the all-time record for most strikeouts in a season with 223 K's last season.

This year, he leads the league once again in strikeouts, as well as perennial leader in swinging strike percentage. He has whiffed on 17.3% of all pitches this season, second place being Ryan Howard at 14.4%. Interestingly, Reynolds does not actually swing at everything a la Jeff Francoeur (60.7% swing percentage) and is barely in the top 50 in percentage of pitches he swings at with 46.8%. This makes it even more amazing that Reynolds leads the league in strikeouts and swinging strike percentage regularly without even taking that many swings. That's a lot of whiffing going on, and I do suppose that the rare times he does connect the bat to the ball, he hits it hard.

I wanted to know more about Mark Reynolds' swinging strike percentages to see how he fares against certain pitch types by handedness. Of the five main pitch types, fastballs, sliders, cutters, curveballs, and changeups, Mark Reynolds has seen cutters less than 200 times since his debut, 139 cutters from right-handed pitchers and 41 cutters from left-handed pitchers. He has seen at least 200 pitches for the other pitch types for right-handed pitchers or left-handed pitchers. Ignoring cutters due to small sample size, I will take a look at Reynolds' swinging strike percentages against four-seam fastballs, sliders, curveballs, and changeups.

Let's take a look at Mark Reynolds' swinging strike percentages against four-seam fastballs split by RHP and LHP (1435 pitches from RHP, 468 pitches from LHP):



Here, it looks like Reynolds falls victim to high fastballs from both right-handers and left-handers. For Reynolds, he whiffs on the outside fastball from LHP stick out as well as the low and inside fastball from RHP.

Here's a look at Reynolds against sliders (1542 from RHP, 224 from LHP):



This is interesting. Reynolds strikes out far more against right-handed pitchers than against left-handed pitchers, but he tends to swing at (and miss) sliders coming from LHP more than he does from RHP. LHP sliders come low and inside while RHP sliders go low and outside, but even LHP sliders coming in from low and outside are swung at and missed by Reynolds.

Curveballs against Reynolds are a whole different story (567 from RHP, 228 from LHP):



Here, Reynolds clearly struggles at connecting on curveballs from right-handed pitchers, some in the strikezone and most low and outside the strikezone. Curveballs from LHP also get Reynolds to whiff sometimes on the inside part of the plate as well as the lower part.

Finally, here's a look at Reynolds against changeups, which look like his greatest weakness when it comes to missing pitches (430 from RHP, 338 from LHP):



This is very telling. The splits against changeups are very different, as Reynolds whiffs on over 50% of changeups from right-handers that are located on the edge of the strikezone at the bottom. This is much different from LHP changeups, where any spot doesn't look to cross over 30% whiff rate, except the lower righthand corner of the zone. What's also crazy about this is that when you look at Reynolds against changeups in general, he misses at around 20% of nearly all changeups low outside and nearly all areas within the strikezone as well.

From these plots, there are characteristics of Reynolds' swinging strikes that are similar to conventional thought and common knowledge, such as chasing high fastballs or low breaking balls. But the key to exploiting Reynolds' weakness at missing the ball when swinging is definitely throwing timely changeups, especially from right-handed pitchers, while it seems that Reynolds is less prone to whiff against LHP curveballs the most.

Roy Halladay's Pitches

Roy Halladay has an array of pitches that he uses, and just got even better this season by modifying his changeup to create a different movement while using it more often. Looking at Halladay's pitch type table at Fangraphs, he is using his new changeup 12% of the time this season compared to less than 5% in previous seasons.

I wanted to take a look at Halladay's different pitches to see which ones he gets the highest percentage of swinging strikes off of. The best step to take in order to compare pitch types would be to generate run value heat maps, but seeing as that I still am experimenting with contour heat maps and local regression models, let's keep it simple first (just in case there are mistakes again). Also, I will be sampling at least 1000 pitches for most of my maps from now on. So instead of looking at his changeups, let's take a look at the swinging strike probability models on Halladay's other great pitches, the four-seam fastball, cutter, and curveball:







Halladay, a right-handed pitcher, gets swinging strikes on high four-seam fastballs against right-handed hitters and high and inside fastballs against left-handed hitters. His cutters go outside on RHH and inside on LHH, getting RHH to whiff on cutters in the zone and LHH to whiff low and inside. Halladay's curveballs are the real meat here in terms of getting batters to whiff, as around 30-40% of curveballs thrown down and away from RHH and down and inside to LHH get batters to whiff.

What can I say? Halladay is one of the best pitchers in our generation, and I haven't even showed the results of his changeup yet. According to Fangraphs' pitch type values for Halladay, his cutter is his most valuable pitch, followed by his curveball, four-seamer, and changeup. But it's his new changeup that's been the most improved since last season, after he made adjustments to the grip on his changeup this offseason.

Corrections to previous Kershaw post

Long story short, I was fine-tuning the regression methods I've been employing to generate those pitch location heat maps, my first example being Clayton Kershaw's slider and curveball. A couple of hours working on this and I realized that much of what was graphed was incorrect (in fact, disregard my previous post). I'm going to reproduce the swinging strike percentage graphs from my last post, which make a lot more sense now (not as high SwStr% values of 60%, smoother plots, down in the strikezone instead of up in the zone, etc.):

These (hopefully) corrected plots still show that Kershaw's sliders induce more swinging strikes than his curveballs. The differences between these ones and the previous post are that the breaking pitches are inducing swinging strikes down in the zone, not up in the zone (the orientation was off in the first post). Needless to say, I regret that I did not mention this in my first post, although I did find the images very fishy. I'm still fine-tuning these sort of local regression models and turning them into surface-fitted filled contour maps. I had several post ideas following the Kershaw one, including a look at Tim Lincecum's pitches and what went wrong this season compared to last season, but I may have to take some time to fully understand the statistics and the method behind the madness of these heat maps before I make a post and include my interpretations again.

Sample size is a huge issue, and I have been informed that looking at a particular pitcher's pitch type may not be suitable for a local regression surface fitting precisely because the sample size is too small (about 200 pitches seems to be too small, especially when modeling swinging strike probabilities where the number of swinging strikes is in the dozens for this particular situation).

Hopefully I don't make this mistake again, but again, I started this blog in order to explore analytical ways of presenting sports information, including graphically, and I'm glad I'm learning a lot along the way.