Jack Flaherty’s Best Pitch Has Been Underwhelming

Jack Flaherty has a 2.83 ERA through seven starts, which comes out to a 73 ERA-. His park adjusted FIP- of 75 is right in line with that figure; his FIP is 3.03. It would be easy to stop there and say Flaherty has been great; his excellent ERA matches up with his FIP, so he must be doing something right. Dig a little deeper, however, and there are some reasons to be skeptical. His overall line has been buoyed by a 7.5% HR/FB. His strikeout rate is down almost four percentage points compared to his last three seasons combined (25.8% versus 29.7%). Worse, his swinging strike rate is down to a below league-average 11.6%, indicating he has been somewhat fortunate to punch out a little over a quarter of the batters he has faced. On contact, things are not much better. His groundball rate is five percentage points lower than it was over those same three seasons and after allowing a below average rate of hard-hit balls from 2018-20, he is now right at league average.

This is all to say that Flaherty hasn’t quite been his excellent, arguably ace-level self (no, I will not be debating the definition of an ace). Poking around, I found an interesting trend. Flaherty has always leaned on his four-seamer and slider, but in 2021, that reliance has accelerated. He is throwing his fastball and slider as a higher percentage of his total pitches than in any other season up until this point. He is increasingly becoming a two-pitch pitcher:

There are two ways you can look at this. First, you could say that he is using his best offerings more often than ever, which can be construed as a positive development. Or you can say that this is making him more predictable, allowing batters to sit on those two pitches, making him less effective. Given that his peripherals are a bit worse this year, one might say that the latter explanation rings true. But his results are as good as ever, so maybe the former point is viable.

Can he be a viable starting pitcher throwing two pitches so often? For context, Flaherty thus far has thrown his fastball 49.6% of the time and the slider 31.1% of the time. That means he is throwing one of those two pitches on 80.7% of his offerings. He does not throw either of his other three pitches (curveball, sinker, and changeup) even 15% of the time.

I took every pitcher season from 2010-20 where the pitcher threw at least 100 innings. I grouped each pitcher by the number of pitches he threw at least 15% of his total pitches and summarized the results:

Performance by Number of Pitches with at Least 15% Usage
No. of Pitches Pitches K% BB% FIP- WAR per 180 IP
1 141 19.0 7.4 101.5 2.15
2 615 20.4 7.2 97.3 2.49
3 572 20.3 7.4 97.4 2.47
4 82 20.0 7.4 98.9 2.36
SOURCE: Baseball Savant

I removed pitchers who threw five or more pitches because there were so few in the data set. The list of pitchers with such a diverse repertoire is very small, something I talked about in my piece on Kohei Arihara. In summary, pitchers who throw more pitches are not inherently better in terms of strikeout rate, walk rate, run suppression, or WAR. I will say there may be some selection bias here. For all I know, throwing more pitches is a value add but it just so happens that the more talented pitchers do not, so I am not properly isolating the effect. With that being said, we are looking at a lot of pitcher seasons and no one group stands out here.

Next I looked at the effect of the third time through the order penalty for pitchers based on how many pitches they threw at a 15% clip. I took the pitch-by-pitch data for all pitches from 2015 through 2020 and used all pitcher seasons where the pitcher threw 100 innings, like above. I took every plate appearance and labeled it by whether it was the first, second, third, or fourth time through the order. I removed the results from the fourth time through the order because the sample was so small compared to the first, second, and third time through given the way pitchers are deployed in this era of baseball. Without further ado, here are the results:

TTO Effect by Number of Pitches with at Least 15% Usage
No. of Pitches 1st Time wOBA 2nd Time wOBA 3rd Time wOBA
2 .312 .327 .340
3 .309 .325 .343
4 .316 .321 .342
SOURCE: Baseball Savant

Not much of a difference here. Maybe this means throwing two pitches so often is not a bad strategy in and of itself because if the pitcher is choosing to do so, it is a signal that those two pitches are much better than anything else in his arsenal.

This information would indicate that pinning Flaherty’s underlying numbers in the early going on being too predictable with this pitch mix lacks merit. That means we need to dig deeper into Flaherty’s pitch performance on an individual level.

Year-Over-Year Pitch Performance
Season Pitch Type Pitch% SwStr% CSW% wOBA
2018 FF 40.0 8.0 27.9 .290
2018 KC 11.2 15.9 35.6 .212
2018 SL 29.9 22.7 35.9 .291
2019 FF 45.2 9.5 28.8 .267
2019 KC 11.7 11.1 32.9 .297
2019 SL 26.5 23.2 35.6 .251
2020 CU 13.6 13.3 27.6 .300
2020 FF 44.2 8.8 33.6 .326
2020 SL 28.7 25.7 36.9 .276
2021 CU 11.0 6.5 19.5 .239
2021 FF 49.6 7.2 27.7 .234
2021 SL 31.1 19.7 33.5 .315
SOURCE: Baseball Savant

The fastball seems fine. The swinging strike rate is down a bit but he has bridged some of the gap by picking up a few more called strikes. His wOBA allowed on fastballs sits at just .234, almost 70 points lower than the past three seasons combined. Given that it has performed slightly worse when you isolate results where the batter does not make contact, Flaherty’s fastball has been the beneficiary of some batted ball luck. According to Baseball Savant, opposing batters are hitting just .149 when they put the ball in play against the pitch. Those results on contact will likely be the main source of regression in Flaherty’s profile. He throws the pitch so frequently (almost 50% of the time) that any outlandish results on it will have an outsized effect on his overall line.

But even if his batted ball luck on his fastball worsens over the course of the season, Flaherty can stave off an improved performance from opposing batters through some better fundamental performance he has control over. That starts with his slider. His slider is generating fewer swinging strikes on the season. After posting rates of 22.7%, 23.2%, and 25.7% in 2018-20, respectively, he is down to 19.7% this season. Not only is he inducing fewer whiffs, the wOBA on the pitch has skyrocketed to .315 (buoyed by a .378 wOBAcon), up 39 points from 2020 and 64 points from ’19.

The slider’s movement profile has not changed much; per Baseball Savant, his horizontal movement is basically unchanged (relative to average) and the vertical movement is down a couple of inches. Part of the reason Flaherty’s whiff rate has taken a step back is the counts he has been throwing the pitch in:

Percentage of All Sliders by Count
Season 0-0 0-1 0-2 1-0 1-1 1-2 2-0 2-1 2-2 3-0 3-1 3-2
2018-20 19.2 10.4 7.4 9.7 8.9 11.8 3.1 6.1 11.4 0.4 3 8.7
2021 17.9 10.1 8.3 14.7 9.6 9.2 1.8 6.9 10.6 0 4.6 6.4
SOURCE: Baseball Savant

A lower proportion of his sliders have come in counts where it is easier to get batters to expand the zone and chase (0-2, 1-2, and 2-2). Over the past three seasons, Flaherty has thrown 30.6% of his sliders in those counts. This season, the figure is at 28.1% (about a nine percent decrease). He is also throwing 51% more sliders after throwing a first pitch ball. Now take a look at his slider’s swinging strike rate by count:

Slider SwStr% by Count
Season 0-0 0-1 0-2 1-0 1-1 1-2 2-0 2-1 2-2 3-0 3-1 3-2
2018-20 15.2 26.8 23 29.5 28.2 18.1 21.4 30.6 21.3 0 25.9 30.4
2021 12.8 27.3 27.8 15.6 28.6 15 25 26.7 13 0 30 14.3
SOURCE: Baseball Savant

Not only is he throwing a smaller percentage of his sliders in counts where the pitcher has the advantage, but his swinging strike rate in those counts (and in a 3-2 count) is down drastically. Worse yet, the increase in sliders following a first pitch ball have not been an effective tactic; his swinging strike rate on 1-0 sliders is down almost 50%.

As I alluded, the easiest way to induce swings and misses is in two strike counts because batters are more prone to chasing. And hitters do not seem to be biting on what Flaherty has to offer outside the zone. Per Baseball Savant, his chase rate is down to 23.8% compared to the league average of 26.9%. The inability to get hitters to expand the zone is evident in the following two heat maps, courtesy of Baseball Savant:

In general, Flaherty is getting the opposition to whiff at acceptable rates given the locations of his pitches, but they are chasing pitches less, especially those way below the strike zone that are almost impossible to make contact with. For his slider whiff rate to tick up, he needs to either work to get hitters to chase, or throw more competitive pitches.

The key for Flaherty going forward is to find a way for his slider, his most dominant pitch, to be more effective. Maybe there is an issue with how his slider and fastball are tunneling with each other and hitters are picking up the slider better out of his hand, since they are chasing less and getting better results on contact. Or he is just so averse to throwing the pitch in the zone right now that he does not have much of a chance to get a sufficient number of whiffs, which would indicate he should challenge batters more. Without digging into the shape and trajectory of his pitches, the former is difficult to say. The latter is more actionable. The slider has been such a great offering throughout his major league career. Trusting it more and challenging hitters by daring them to swing when he drops it in the zone might be a way to more efficiently strike batters out and keep balls from going in play. If this is the case he will not have to rely on his defense turning batted balls into outs. The issue has not been getting to advantageous counts more often; though his first pitch strike rate is down to below league average (54.0%), his percentage of pitches in two-strike counts is largely unchanged from 2018-20 (0.2 percentage points). He is almost getting all the way there (with regards to generating strikeouts), he is just missing that final piece in finishing hitters off.

I say all this acknowledging that the surface-level results have been excellent for Flaherty in his first seven starts. There is nothing taking that away from him; those great starts are already in the bank. But if he wants to continue that level of performance, he needs to get back to piling up swinging strikes with his slider like he has in the past. With that will come an increase in his strikeout rate, one more in line with his career norm. Again, this is not to say he has not been good in his first seven starts. I will admit that I am nitpicking his performance. But I know Jack Flaherty is one of the best starting pitchers in baseball. He has the type of stuff that should place him towards the top of the strikeouts leaderboard. This whole exercise is about identifying tweaks he can make to to fulfill his status as one of the league’s premier strikeout artists. If he makes the necessary physical or strategic corrections to how he’s deploying the pitch, I have no reason to think he can’t continue to put together a great 2021, with a pile of punch-outs that is supported by the underlying data.

Carmen is a part-time contributor to FanGraphs. An engineer by education and trade, he spends too much of his free time thinking about baseball.

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2 years ago

I love articles like these that dig beneath surface level performance and talk about underlying stats that might be cause for optimism or concern. It has seemed to me for so long that baseball is just kinda random. Players get better and worse for seemingly no reason and you just have to roll with it. Now with all these crazy alphabet statistics there’s an entire new level to the game that wasn’t explored before. Thank you for the interesting read!