Last week, I laid out some broad categorizations of what makes a slider effective, when viewed in the aggregate. As a quick recap: The most important single characteristic is hitting the corners of the strike zone. If you have a slider with plus horizontal movement, it’s also okay to miss over the middle of the plate. The middle of the plate is a great location early, but a poor location late in counts. There’s more, but those were the key findings.

That analysis left some additional factors out, because there are only so many tables you can fit into an article before it all starts to look the same. Additionally, some of those factors are beyond the scope of this analysis. Sequencing and tunneling, for example, are too complex to reduce to a two-dimensional grid. Deception might be even more confusing; I’d struggle to quantify it at all, let alone simplify it into a few buckets for analysis.

Today, I’d like to look at the rest of the factors I found easy to quantify and analyze. First, let’s talk about pitch movement. Last week, I looked at horizontal movement, because that’s the classic action we associate with a slider. It’s not the only type that pitchers throw, however. Sliders are such a broad category of pitch that they encompass pitches that mostly break sideways, mostly break down (at least, relative to a fastball), or have some mixture of the two.
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Not everyone is interested in projecting the future, but one common thread in much of modern analytics in this regard is the attempt to describe a volatile thing, such as a play in baseball, using something less volatile, such as an underlying ability. This era arguably began with Voros McCracken’s DIPS research that he released 20 years ago to a wider audience than just us usenet dorks. Voros’ thesis has been modified with new information, and people tend to say (mistakenly) that he was arguing that pitchers had no control over balls in play, but DIPS and BABIP changed how we looked at pitcher/defense interaction more than any peripheral-type of number preceding it.

One of the things I want to try to project is what types of performance lead to the so-called Three True Outcomes (home run, walk, strikeout) rather than just tallying those outcomes. For example, what type of performances lead to strikeouts? I’m not just talking about velocity and stuff, but the batter-pitcher interactions at the plate — things like a pitcher’s contact percentage, which for pitchers with 100 batters faced in consecutive years from 2002 has a similar or greater r^2 to itself (0.53) than either walk rate (0.26) or strikeout rate (0.51) does. Contact rate alone has an r^2 of 0.37 when comparing it to the future strikeout rate.

As it turns out, you can explain actual strikeout rate from this synthetic estimate quite accurately, with an r^2 in the low 0.8 range.

Statcast era data works slightly better; the version of zSO which has that data is at 0.84, and the one that predates Statcast data is at 0.80. Cross-validating using repeated random subsampling (our data is limited, as there’s no “other” MLB to compare it to) yields the same results.

Like the various x measures in Statcast, these numbers shouldn’t be taken as projections in themselves. While zSO projects future strikeout rate slightly more accurately than the actual rate itself does, a mixture of both gets a better r^2 (0.59 for the sample outlined above) than either does on its own. Looking at zSO alone as a useful leading indicator, however, gives us an idea of which players may be outperforming or underperforming their strikeout rates so far this season. All numbers are through Wednesday night.

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In eight of the 12 different count-states, fouls and whiffs come with the same penalty: a strike. In a 1–1 count, for example, it really doesn’t matter whether you look silly swinging and missing at a curveball or just miss a home run by being a few inches wide of the foul pole. In either case, hitters have to come back for another swing, with the count now 1–2.

We all know this. Those are just the rules of the game. But it creates a very interesting hierarchy for hitters. When a hitter swings, only one of three things can happen: He can put the ball in play, foul it off, or whiff. And, as mentioned, for two-thirds of those outcomes — the foul and the whiff — no distinction is even made in eight of the 12 count-states. No wonder that the league-average hitter, by run value, is penalized when he swings.

But fouls have a unique property that makes them wholly different than whiffs: the ability to prolong at-bats. In the same way that you can’t lose on a serve in ping pong, you can’t strike out on a foul ball (bunts excluded). While they carry the same penalty as whiffs in all non–two-strike counts, foul balls manage to be the only safety net for hitters when their backs are against the wall, and to me, it makes for a pretty interesting dichotomy when you break it down that way.

Because foul balls provide this special safety net for hitters, it would make sense intuitively that hitters who foul off more pitches probably strike out less. If a hitter fouls off a lot of pitches, especially relative to the number of whiffs he creates, he is almost certainly going to avoid a K and eventually should get a pitch to put in play. Indeed, there is a pretty strong correlation between foul-to-whiff ratio and strikeout rate:

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What’s the most important characteristic of a slider? Let me show you a table:

There are two things that might need explaining in here. The attack zones are Baseball Savant’s way of cutting the strike zone up into granular pieces, and I think they’re neat. They look like so:

Run values are from the batter’s perspective, so that -785 runs in the shadow zone means that batters have been 785 runs below average — what they’ve done on all pitches across the whole year — when they faced sliders in the shadow zone. In other words, sliders on the corners of the plate have been excellent — not really a shock.

What’s the most important characteristic of a slider, then? Well, allow me to show you a different table:

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If you are a regular FanGraphs reader, chances are that you’re aware of the rise in strikeouts across the majors. At this point, bemoaning the rise in strikeouts is an essential component of the baseball media apparatus. Every season is accompanied by pieces on the subject. I found this type of article going as far back as 2013, and they have been especially prevalent in recent seasons. It seems to be a rite of passage to put out a piece on the increasing strikeout rate, so as a newly minted member of the baseball writing community, here is my entry in the genre.

For context, the league-wide strikeout rate has increased every season since 2005, when it sat at 16.4%. In 2021, that figure has risen to 24.1%. That is a 47% increase in 16 seasons. Not only has the strikeout percentage monotonically increased, but the rate at which it is increasing is growing. From 2005-09, the rate increased by 9.7%; from 2010-14, 10.3%. In the most recent five seasons, the strikeout rate increased by 11.6%.

The question is always who and what is driving this phenomenon, and the answer is almost always “well, there are a few factors at play.” One angle that I thought has been under-researched is hitter behavior with two strikes. You may have heard your favorite local newspaper columnist bemoan the idea that hitters do not have a two-strike approach anymore, that all they try to do is hit home runs, which has led to all the strikeouts. Of course, this type of thinking is reductive, mostly because it does not even consider the role of the pitcher. Nevertheless, many have discussed two-strike results, though more anecdotally than quantitatively. So let’s investigate this aspect of the strikeout rate problem first. The following is the strikeout rate and wOBA in plate appearances that reach two-strike counts in the Statcast era:

Like the overall strikeout rate, the strikeout rate in these plate appearances is monotonically increasing but much more slowly. Year-over-year, the increase never exceeds 2% besides this season and 2020 (about 3%). I will note we are only about a month and a half into the season and given the weather, league offense is at its nadir, so I would expect this to regress some. wOBA with two strikes has jumped in the Statcast era and this season so far has stuck out like a sore thumb. The weather caveat applies here also, as does the caveat that we are dealing with only a fraction of the plate appearances in 2021 versus all other seasons besides 2020 (for obvious reasons). This information seemingly debunks the awful two strike approach theory, at least within the defined time frame. Hitters are barely striking out more when they get to two strikes and their overall performance has not changed much season-over-season, 2021 notwithstanding. If we dig further into two strike behavior, the idea that hitters have drastically changed when they are confronted with two strikes does not track:

I will note that the chase rate calculation is based on my own filtering of the Statcast data from Baseball Savant. The swinging strike rate has increased every season and the rate at which balls are put in play with two strikes has decreased every year, which gives some credence to the complaint about hitter behavior. I would argue the changes are so small, however, that drastic claims about today’s players are not warranted. We are talking about 1.3 percentage points in terms of swinging strike rate, and 2.2 percentage points in balls in play rate from 2015-21. I do not think anyone without access to this kind of statistical information can really tell the difference between those figures when watching the game. The swing rate with two strikes has been very stable in this era. In terms of chase rate, batters have become more discerning, which can only be construed as a positive development, assuming we believe it’s better to have fewer strikeouts.

Interestingly, the rate of called strikes as a percentage of total two-strike pitches has seen a noticeable jump in 2021. Devan Fink wrote about how pitchers have become more aggressive throwing the ball in the zone this season with the advent of the new ball. I would imagine this is the impetus for the growth in the percentage of strikeouts via the called strike.

Overall, the differences in two-strike performances between seasons do not seem substantial enough to explain the acceleration of the strikeout rate growth. Maybe it is not batter performance in two strike counts, but instead a notably higher percentage of total pitches being thrown with two strikes?

There is basically no difference between 2021 and the preceding five seasons combined. The count-based run values are more of a mixed bag with no discernible trend.

Two strike performance changes does not seem notable in recent vintage. In fact, the swinging strike rates in all counts have effectively increased at the same rate across all counts.

The last thing I investigated was looking at pitch types and seeing if any groups of pitches are more responsible for the rate of whiffs than the others. Here there are more interesting trends.

Neither breaking pitches nor offspeed pitches have seen much of an influx in swinging strikes. Hitters have struggled more with fastballs, on the other hand, in all situations. (Another hat tip to Devan Fink, who wrote about the unusually large increase in fastball velocity in the month of April this season.) Pitchers’ fastballs are becoming tougher to time-up and now that they are becoming more aggressive throwing the ball in the zone, they are inducing more swinging strikes with those pitches.

The league’s two-strike approach does not seem to be having an outsized effect on the rise in strikeouts, at least in this most recent era of baseball. There are small upticks in a few relevant metrics, but more of the increase has to do with swings and misses in all counts, especially on fastballs. This count-based analysis yielded similar results to an excellent piece from Chet Gutwein here at FanGraphs. He found that not only has the league’s swinging strike rate on fastballs increased more relative to other pitch types, but fastballs high in the zone were mostly to blame due to the continuing growth of velocity and, as a consequence, spin rate.

As the league tries to address the issue of fewer balls in play now and in the future, finding a way to combat the rise in pitcher velocity should be one of the first items on the docket. The fact that pitches are moving more than ever does not appear to be as large a factor, given the changes in whiff rates on breaking and offspeed pitches. Moving the mound back, which will be implemented in the Atlantic League this season, and giving hitters more time to react seems like a good start. After parsing through the two strike data, it seems like rectifying the lack of formidable two strike approaches across the majors is not the silver bullet many believe. Digging further into the data by pitch type in all counts, the main issue is rising whiff rates on fastballs, which Chet Gutwein opined on in his own piece I referenced above. So maybe combating velocity is the elusive silver bullet? Without a relatively controlled experiment we cannot say for certain. But we can say that hitters being criticized for forgoing any semblance of a two strike approach and placing the blame on them for the rise in strikeouts is most likely a futile exercise.

Last week, I investigated something that I’ve long wondered about: are relievers particularly prone to wildness on their first batter of the game? I didn’t find much of an effect, and I also got tons of valuable feedback about further avenues for investigation. Do base/out states matter? Does handedness matter? Do intentional walks skew the data?

Aside from the last one (a definite yes), I haven’t explored all of these avenues yet. I did, however, answer another question I was curious about, one that ties into the general theme of reliever walk rates. I’ll tell you upfront that I found a confusing result, and that I’d love to hear anything I’ve missed or avenues for further investigation.

Here’s the question I’m answering: when a reliever walks the first batter he faces, what does that tell us about the rest of his appearance? All of us have seen this in practice, and we probably all know the existential dread it engenders. Great, he doesn’t have his command today. How many walks are coming up? Is the lead safe? Will the team even stay in the game long enough for a new pitcher comes in?

To explore this possibility, I examined every game thrown by a reliever since the beginning of the 2015 season. I split each reliever’s appearances into two subsets: every appearance where they unintentionally walked the first batter they faced on one hand, and every other appearance (except intentional walks, I threw those out) on the other. This gave me a sample of 1,085 relievers across more than 80,000 appearances. Read the rest of this entry »

Pitchers are always looking to chip away at the platoon advantage. Two of the most common weapons in doing so are the changeup and curveball. The former fades away from opposite-side batters and from the barrel as the bat whips through the zone. Most of a curveball’s movement, meanwhile, is vertical; no matter the handedness of the batter and corresponding bat path, the pitch can duck under the bat as the batter makes contact. Sliders, though, generally have a large platoon split, to the detriment of the pitcher, as they move more horizontally relative to vertically and toward the pitcher’s glove side. This leads the ball towards the barrel of an opposite-handed hitter, giving him more of an opportunity to make contact.

Cutters are interesting in this regard. Given the movement of the pitch, you would expect it to have significant platoon splits like a slider. The ball moves toward a pitcher’s glove side, albeit generally not as far as a slider; an opposite-handed hitter would have a better chance putting the barrel on it. But this is not the case, according to research from Max Marchi done back in 2010, as he found that cutters were in the middle of the pack with respect to pitch-type platoon splits. It still had more favorable splits when the batter had the platoon advantage, but that is the case for all pitches in general.

So why does the cutter not have much of an effect on the platoon advantage despite its break? As MLB.com explains it, the magnitude of the horizontal break is subtle enough to catch a hitter expecting a four-seamer off guard. Thus, when he swings, the movement of the pitch forces the batter to fight it off his hands and either induces weak contact or breaks the bat altogether. My thesis was that players are turning to the cutter because of these neutral platoon splits, as heavily using a pitch that works well to hitters from both sides makes you harder to predict. Read the rest of this entry »

There have been some scary moments in the first few weeks of the 2021 major league season. On April 28, Phillies Manager Joe Girardi was ejected after both Didi Gregorius and Bryce Harper were hit by pitches while they were playing the Cardinals. Harper’s incident was particularly scary as he was hit in the face with a 97 mph fastball. On April 5, Cubs catcher Willson Contreras was plunked by a 93 mph fastball to the helmet. Two days later Reds rookie Jonathan India had a similar moment after a fastball ricocheted off his helmet.

It’s not your imagination: batters are being hit by wayward pitches at a record clip. Ken Rosenthal of The Athletic made note of the trend this morning. Baseball Prospectus’ Rob Mains recently published an excellent breakdown of this year’s record-setting pace for hit batsmen. I was particularly taken aback by this chart showing that prior to 2018, no season in baseball history had a hit batsman in more than 1 in 103 plate appearances:

Mains continues:

There was one batter hit per 96 plate appearances in 2018, a new record. It fell further, to 94, in 2019. Then all the way to 81 in last year’s short, weird season.

This year? Through Tuesday night’s games, it’s down to 74.5. Batters are being hit thirty-eight percent more frequently than in 1901. There are just over eight hit batters for every five just a decade ago. We’re averaging 0.997 hit batters per game in 2021, a single HBP shy of one per game—a level the sport’s never approached. Batters so far have a .309 on-base percentage. Hit batters account for thirteen points of that figure. Ten years ago, there were only eight points of hit batters in MLB’s .321 OBP.

I wanted to take a look at possible reasons the HBP rate is at record levels so far in 2021, but first we need to be clear about which parts of this trend are continuations from previous seasons and which parts are actually new. In 2019, Devan Fink demonstrated that the HBP rate per plate appearance was approaching the highest levels seen since the early 1900s. He looked at increased velocity and reliever usage to demonstrate that while a pitches’ speed didn’t necessarily mean a pitcher had worse command, relievers had a larger share of HBP than their starting counterparts. Read the rest of this entry »

On Wednesday afternoon, Liam Hendriks entered a tough situation. There were two outs in the bottom of the ninth, but his margin for error was nonexistent. The bases were loaded, and the White Sox were locked in a tie game. One hiccup in command, four slightly misplaced pitches, and the game would be over.

Do pitchers have less command when they enter? Is it worth worrying about whether a pitcher might not have it that day? I have no earthly idea, so I decided to investigate. First things first, though: I wasn’t actually sure what I was investigating. Time for some experimental design.

What about the walk rate, but only on the first batter faced by a new reliever? That’s certainly a number I could look up. That checks in at 8.1% from 2015 to present (I used the Statcast era even though there’s no Statcast data involved in this query, just for consistency’s sake). Over the same time frame, the overall reliever walk rate is 9.3%. Case closed, let’s go get brunch.

Only, that’s a bad comparison. We’re not comparing apples to apples. If we’re actually going to look into whether pitchers are particularly likely to come in and not have it, we need to compare like to like. Take the immortal Sugar Ray Marimon, who made 16 appearances for the Braves in 2015. He was a one-hit wonder, though “wonder” might be strong: he compiled a 7.36 ERA in 25.2 innings before decamping to Korea. Read the rest of this entry »

On Monday, I examined the new baseball’s impact on April home run totals. In sum, home runs were down in April 2021 compared to April 2019, with the home run per batted ball rate dropping by roughly 0.45 percentage points, a figure that would result in about an 8% decrease in home runs from ’19 to ’21, under the assumption that hitters receive roughly equal plate appearances in each season. (Due to seven-inning doubleheaders and the new extra inning rules, though, that won’t happen, but it’s still good to compare apples-to-apples to estimate the impact.)

After sharing the article on Twitter, I received an interesting question that I felt merited further discussion: How many of those now-non-homers turn into hits versus outs? That is a fascinating question because it potentially gets to the heart of why MLB dejuiced the baseballs in the first place. Baseball didn’t want to eliminate offense, per se; they just wanted to alter how it is generated, with more balls put into play rather than what they perceived as a recent over-reliance on the long ball. In short, if all of those newly-created non-homers are now other types of hits, then dejuicing the baseball might’ve actually had the impact MLB wanted. If they are now outs, then it’s just going to make life that much harder for batters.

Given the majors’ historically-low batting average this season — once again, I’ll point you to Brendan Gawlowski’s excellent piece on the matter — you can likely guess what happened: Outs are up. Read the rest of this entry »