Underthrown Pitches And The Pitchers Who Underthrow Them: Putting It All Together

Over the last several weeks, I’ve scoured Baseball Prospectus’ PitchF/x leaderboards for the league’s underthrown pitches. We’ve covered two different pitch types each week starting with four-seam fastballs and sinkers in the first installment, cutters and curves in the second, and sliders and changeups last week. This week, we put it all together. Now that we’ve identified the most underthrown pitches, who should consider overhauling his entire pitch mix to make the most of his electric stuff?

For a refresher on results and methodology, check the links below.

Vol 1: Four-seamers and Sinkers

Vol 2: Cutters and Curves

Vol 3: Sliders and Changeups

In an effort to be shall we say, less inert, I’ve done a few things differently this week. In addition to considering ground balls, pop-ups, and whiffs, I added an element of control in arriving at a Pitch Score. Specifically, I incorporated called strike-to-ball ratio. Over the last several weeks, I’ve waffled on whether to do this as many pitches, particularly the most effective out-pitches, are often purposely thrown outside of the zone. Think of a spiked curve or running slider.

Still, stealing called strikes is undeniably a desirable quality and should be incorporated at some point provided there’s a correlation with pitching outcomes. And it turns out there is.

Now, in the process of assessing pitch mix effectiveness, I also calculated Arsenal Scores. I’m certainly not the first to do this. Eno introduced arsenal scores almost a year and a half ago and Alex Chamberlain arguably improved upon them by weighting each pitch by frequency thrown. In previous articles in this series, I didn’t weight Z-scores differently based on their correlations as Eno did originally, nor by pitch frequency as Alex did subsequently. This time however, I’ve assigned weights based on a model regressing whiffs, grounds-plus-pop up rate, and called strike-to-ball ratio against Baseball Prospectus’ True Average statistic.

As for weighting based on pitch frequency, I made a conscious decision not to do so because this analysis is less concerned with “as-is” and more interested  in “what could be” if a pitcher threw his best offering at a frequency commensurate with its effectiveness.

Below you’ll find the pitchers who should consider a major overhaul to their pitch mix. For each pitcher, I’ve totaled the Underthrown Indexes (UI) of all offerings with a positive Pitch Score, ignoring any that graded out negatively. A negative Pitch Score results in a negative UI suggesting a pitch is actually overthrown. Any pitch with a positive UI should be thrown at the expense of one with a lower but preferably negative UI.

Additionally, because the denominator in UI is frequency, a negatively graded pitch thrown rarely will result in a more negative UI than the same ineffective pitch thrown too often. A very negative UI doesn’t mean the pitch is being thrown too often; on the contrary, it means that the pitcher, provided he chooses to throw a poor pitch at all, does so judiciously.

A high Arsenal UI can be a function of two things. The first is a poor pitch mix; pitchers who underthrow their best offerings will have a high UI. Another factor that leads to a high Arsenal UI is overall arsenal quality. If a pitcher features four above average pitches, all four will yield positive UIs. So while Corey Kluber might bring down his Arsenal UI slightly by throwing his sinker less frequently in favor of his cutter, slider, or change, he’ll still feature an elevated aggregate Underthrown Index because the latter three pitches rank 1^st, 4^th, and 4^th among their respective pitch types in Pitch Score; in other words, they’ll always be considered underthrown.

Takeaway #1: Corey Kluber is really good.

Takeaway #2: So is Trevor Cahill. Cahill features the league’s 3^rd best curveball, 4^th best slider, 10^th best changeup, and 25^th best sinker. That’s four, count ‘em, four elite or above average pitches from a 29-year old journeyman who’s spent time in the minor leagues each of the previous 4 seasons for non-rehab related reasons. In fact, Trevor Cahill leads the league in Arsenal Score. What I wouldn’t give for a second chance at my Bold Predictions right about now…

Now, those pitches also happen to be the league’s 12^th, 3^rd, 12^th, and 32^nd most underthrown pitches within their respective classifications. Like Kluber, Cahill is another example of a pitcher whose high UI is supported not by poor pitch selection but rather by a robust and effective arsenal. Having just made his second rehab start last night in his return from a shoulder strain, this is likely your last opportunity to buy.

In a two-start span against the Brewers and Rangers, Jacob deGrom allowed 15 earned runs, 6 walks, and 4 homers in just 8 innings. He watched his ERA balloon from 3.23 to 4.75. He’s also been spectacular since. Over his last three starts, deGrom has averaged 8.1 innings, a 0.72 ERA, and 54.7% ground ball rate. Now, it’s worth mentioning he’s also stranded 99% of his base runners and benefited from a .156 BABIP.

But regardless of whatever peaks and valleys owners may endure with deGrom, the fact is that he boasts one of the best arsenals in the game. And it’s one that could be made even better by throwing his sinker and curve more often at the expense of his slider. The former rank 8^th and 26^th among their respective pitch types while his slider ranks just 48^th. And what do you know, that’s exactly what he’s done since those two blow-up starts just a couple weeks ago.

Whether this trend continues is anyone’s guess, however deGrom has to be encouraged by the results his last three times out.

I mentioned Ariel Miranda’s slider last week. For an extreme fly-ball pitcher who doesn’t miss many bats, a pitch that generates grounders, pop-ups, and whiffs should be an often-pulled arrow from his quiver. This is especially true given the rest of his arsenal’s mediocrity. Miranda’s slider ranks 23^rd in whiffs per swing and 3^rd in grounders-plus-pop ups per ball-in-play combining to give him the 14^th best slider in the game. He should also consider leaning on his changeup a bit more as well as it ranks 35^th out of 140 qualified change pieces. Really, Miranda should throw anything that keeps the ball out of Safeco’s outfield bleachers and both his slider and change do just that.

Between injuries, inconsistency, and  adolescent crushes made very public, we’ve yet to see the Matt Harvey of old. Sadly, we may never see him again (although if you’re partying in Montauk these days, there’s a good chance you already have). The list of successful returns from the ailment that plagued him is and remains depressingly short.

Harvey’s Arsenal Score ranks 89^th out of 211 qualified pitchers. That he continues to throw a slider and changeup that rank 93^rd and 104^th among their respective pitch types nearly 35% of the time hasn’t done him any favors. Harvey has also given up an uncharacteristically high number of homers this year.

Perhaps leaning more heavily on his sinker and curveball, both of which he rarely throws, would help him generate more ground balls and pop-ups. We may never see The Dark Knight rise again, however that doesn’t mean Harvey can’t reinvent himself as a contact-manager and, health willing, still lead a productive career.

There are plenty of pitchers who could benefit from altering their pitch mix a bit. Danny Salazar should consider incorporating his slider a bit more. I’d say the same of Max Scherzer and Dallas Keuchel but whatever they’re doing appears to be working just fine.

Marcus Stroman and Drew Pomeranz should go back to their cutters. Both are elite at inducing whiffs and better than average at burning worms. Stroman’s will also steal called strikes as well.

Zack Godley and Tyler Chatwood could each stand to throw more changeups. Godley already features top-10 swinging strike and ground ball rates so it’s scary to think what a few more changeups at the expense of his cutter could do.

Chatwood doesn’t boast nearly the arsenal that Godley does but his changeup is every bit as good, if not better. He’s had issues with homers and throwing his changeup a bit more could take care of that.

I had planned to talk about Arsenal Scores but I think that might deserve its own article so look for that next week. Still, in case you might find it useful, I’ve included a list of the Top 100 arsenals following the UI leaderboard. How crazy is it that Brandon Finnegan, who only threw one pitch that qualified for this exercise sits in the Top 10? By Pitch Score his sinker has been the best pitch in baseball by a YUGE margin. Here’s hoping for a speedy recovery. Again.