How (Not) to Set Up a Fastball

Pitch sequencing, in my opinion, is the next big thing in the field of baseball research, and despite what Samsung might like to tell you, it isn’t here yet. There has been some tremendous work done, but we’re still a long ways away from aggregating findings into one clearly defined picture of how pitch sequencing exactly works.

But we might as well continue to add to the findings. I looked at one aspect of pitch sequencing – shifts in the called strike zone – last month. Next, I’m looking at how best to set up different types of pitches. We’ll start with four-seam fastballs, and, so as to keep it simple for now, focus just on the fastball and on the pitch immediately beforehand. Not pitches before that in the same at-bat, not pitches to the same batter earlier in the game, not pitches to that batter from a different game.

Intuitively, you might expect changing speeds on the batter to be an effective way to mess with their swing and timing. A changeup, then, should be a good pitch to set up a fastball – changeups are generally 10-plus mph slower than the same pitcher’s fastball. Curveballs, too, should be decent setup pitches, as should sliders to a lesser extent. (Sliders are usually thrown harder than curves.) As it turns out, though, it doesn’t quite work that way.

Contact% = Foul balls + balls in play per swing

There’s some year-to-year variation, but, by and large, changeups are ineffective ways to get swings and misses on the fastballs which follow them. Now, bear in mind, the scale here isn’t so large – it’s a few percentage points each way. But it’s still pretty clear that changeups, as well as curveballs, don’t help the pitcher throw a better fastball the next pitch.

Meanwhile, sliders and fastballs are much better. In short, a batter is more likely to swing and miss at the second fastball in a row than they are at a fastball that comes immediately after a changeup. (Note: the fastball category for the first pitch includes all kinds of fastballs – two-seamers, cutters, etc. – not just four-seamers. There wasn’t really much of a difference among them all, and the graph looks a lot cleaner with only four lines.)

This seems very counterintuitive, so there are surely some biases we’re missing, right? Maybe the pitchers who throw two fastballs in a row have better fastballs and are weighing down the contact rate by adding lots of fastball-fastball swing and misses. Maybe two fastballs in a row means that the second one is more often in a location where it is difficult to make contact, such as outside the strike zone. (League-average contact rate is 85% within the strike zone and 61% outside of it.) Maybe the second consecutive fastball is more likely to be thrown in a two-strike count, where batters have to protect the plate, and a fastball preceded by a changeup is more likely to be thrown in a three-ball count, where batters can swing at what they want.

Again, as it turns out, that’s not the case. None of those possible explanations really work. The only one that comes close is the first one, that the fastball-fastball sequences are being thrown more by pitchers with good fastballs, so the contact rate on the second fastball will be lower. Here’s a graph that supports that point:

Fastball-Fastball% = percentage of two-pitch sequences in which both pitches were fastballs; grouped by pitcher; 2015 only

The more times a pitcher threw two consecutive fastballs (where, again, the first was any kind of fastball, not just a four-seamer), the better that second fastball did contact-wise. Note, however, that (a) the effect is small and (b) the average pitcher, not weighting by number of pitches thrown, has a higher contact rate on fastballs that follow changeups anyways. Without weighting, we can be sure that no one small subset of pitchers (i.e. those who throw a lot of fastballs and get a lot of swings and misses) is heavily affecting the scale.

The other explanations actually work against our intuition and support the first graph. For one, fastballs that follow fastballs are actually thrown in the strike zone much more often than fastballs that follow changeups.

Again, contact rate in the zone is 24 percentage points higher than out of the zone, so seeing fastballs at the top of this graph indicates that maybe the contact rate on fastball-fastball sequences should be even lower. In 2015, fastball-fastball contact rate was at least three percentage points lower than changeup-fastball contact rate for both pitches inside and pitches outside the strike zone.

And, lastly, fastball-fastball sequences are more often thrown in counts where the expected contact rate is much higher than changeup-fastball sequences, once again indicating that perhaps the fastball-fastball contact rate should be even lower. Two graphs:

Second pitch of the sequence only

Fastball-fastball sequences are thrown in three-ball counts more often than changeup-fastball sequences are. Changeup-fastball sequences are thrown in two-strike counts more often than fastball-fastball sequences are. As the following table suggests, that should favor the changeup-fastball sequences in terms of producing swings and misses.

Two-strike counts lead uniformly to lower contact rates than three-ball counts. And yet, despite that, fastball-fastball sequences manage to produce a lower contact rate, year in and year out. Furthermore, fastball-fastball sequences have a lower contact rate than changeup-fastball sequences both with three balls and with two strikes.

Of course, contact rate isn’t everything. It’s an important thing for sure, but what if the contact that is made on those changeup-fastball sequences is better contact than on the fastball-fastball sequences?

wOBABIP = wOBA on balls in play

Ok, good, just checking. There’s a lot more year-to-year variation than with contact rate, but fastballs come out on top here, too — or bottom, depending on which way you look at it. Changeup-fastball sequences lead to harder contact, or at least a higher wOBA on balls in play, than fastball-fastball sequences do. Of course, there is also more than just contact rate and wOBA, but those are probably the most important two. (For those wondering, there’s barely a difference in swing rate.)

The lesson: fastballs set up fastballs well, changeups do not. That’s not to say, of course, that changeups are useless pitches. They are better at generating swings and misses than fastballs are, and, when disguised well, they can be effective at tricking the hitter and getting him to swing early. But they aren’t any good at priming the batter to swing and miss at a fastball the next pitch.