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What Makes Jack Flaherty so Special?

The Cardinals have a burgeoning ace. What are the keys to his success?

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MLB: Milwaukee Brewers at St. Louis Cardinals Scott Rovak-USA TODAY Sports

With most of the game’s elite pitchers, it’s fairly obvious why they’re elite. Noah Syndergaard, Aroldis Chapman, and Luis Severino boast high octane fastballs. Justin Verlander, Clayton Kershaw, Trevor Bauer, and Gerrit Cole use tremendous spin on their four seam fastballs to get cheap, easy strikes at the top of the zone. Corey Kluber also has great spin and commands it as well as just about anyone. Max Scherzer does... well, just about everything extraordinarily well. Then there’s today’s starting pitcher, Jack Flaherty.

You see, Flaherty’s ranking in a lot of these metrics is absolutely fine, but not elite. His velocity is fine. His four seam spin is below average. If you look at his command score on Baseball Prospectus, it’s below average- 107th out of 140 pitchers with 100+ innings last year. For instance, here’s his percentile rank in a lot of these categories via Baseball Savant:

Yet Flaherty’s actual results in 2018 and spring training this year have been thrilling. His strikeout percentage, 28.5%, was the fourth highest for any rookie with 150+ innings, behind only Dwight Gooden, Hideo Nomo, and Kerry Wood. Look at the K%, expected slugging percentage, and expected weighted on-base average in that graph above. He was well above average in limiting damage and racking up strikeouts.

I thought it’d be instructive to look at exactly what makes Flaherty so special. How is he this effective if neither his raw velocity or spin rates are elite?

The Repertoire

The story of Flaherty’s dominance begins with the depth of his repertoire. He throws a four seam fastball, sinker, curveball, slider, and changeup. Admittedly, he didn’t use the changeup much last season- just 3.1% of the time- but it’s in his arsenal. Simply throwing lots of different pitches is only part of the story, though. What good does it do to throw a curveball if it’s basically pus coming out of the hand?

Here’s where Flaherty’s arsenal stands out. Here’s the xwOBA against each of these pitches for Flaherty, and his percentile rank amongst all pitchers with 1500 pitches thrown last year:

Jack Flaherty Pitch Quality, 2018

Pitch xwOBA Pctile
Pitch xwOBA Pctile
4-Seam 0.299 79.86%
Slider 0.255 50.00%
Curve 0.177 93.80%
Sinker 0.344 50.75%
Change 0.178 96.32%
Data via Baseball Savant. Percentiles amongst all pitchers with minimum 1500 pitches in 2018.

All five pitches were at least average in suppressing production in 2018. Three of them are upper quartile and it doesn’t even include his best pitch- his slider. More on that soon.

It’s hard for a hitter to react when a pitcher has five quality pitches he can throw at you, especially when three of them are upper quartile effective.


If you’re unfamiliar with tunneling, or if you just want a refresher, I highly recommend Andy Schrag’s brilliant piece about it here last spring. The general gist of tunneling is that pitchers want to make each of their pitches look as similar as they can right up until the last moment a hitter decides that he has to swing. The more similar they look up until a hitter has to decide, the more effective they are when they’re different after the hitter decides. It’s especially true for certain combinations, such as a sinker- which dives down and a little to the hand-side for a righty- and a slider, which has more of a lateral break to the glove side. There’s also not much of a difference in velocity in those two pitches, making tunneling an important ingredient for success.

Enter Flaherty. Compare and contrast how his sinker looks:

and how his slider looks:

In Flaherty’s case, he’s the 20th best out of 146 pitchers tunneling his slider-sinker combo (30 times min.) against righties. Flip the order (sinker then slider) and he’s 35th of 99. Now, keeping in mind that he tunnels those two pitches off each other very well, go back and look at those videos. Think about a hitter trying to react to those pitches against a pitcher who conceals them well above average.

It gets better. Here’s how his curveball (technically a knuckle curve) looks:

Now imagine that pitch pairing off of a fastball, another combo he tunnels extremely well particularly against lefties (6th best in all of baseball last year, and 15th best in the curve-then-fastball combo). If you’d like to see the two together, the incomparable @cardinalsgifs put this pair together:

Gif via @cardinalsgifs

Flaherty is also flirting with using the changeup more, which the also-incomparable Joe Schwarz discussed late last season. He doesn’t throw it much, but it tunnels extremely well with his slider. It also mimics his sinker at a lesser speed, making it a devilish weapon in his repertoire to disrupt timing.

Side note: you can learn a lot about pitching from @cardinalsgifs, Joe Schwarz, and Michael Augustine, amongst so many others

Avoiding Danger

The last thing I’ll discuss today is how intelligent Flaherty is in avoiding his danger zones. We can show this with two simple charts, one vs. lefties and one vs. righties. All of these graphs come from Baseball Savant. First, righties:

Over a quarter of his pitches are thrown in the zone with his second lowest exit velocity allowed. He’s throwing 58% of his pitches to righties in zones where they have an average exit velocity against him under 82 mph. In other words, 58% of the time, he turns righties into Wilmer Difo or Magneuris Sierra, most of them lacking the speed of either of those players. On the flip side, less than a quarter of his pitches are going in the most dangerous zones (middle of the plate, and up and away).

Here’s the same exercise against lefties:

The effect isn’t quite as pronounced as it is vs. righties, but his danger zones aren’t nearly as dangerous, either. There are only two zones where he’s yielding over a 90 mph exit velocity, and only 13 total percent of his pitches went there- middle of the plate, and middle outside, the same two spots that lefties hit against everyone.

There’s a missing piece to the lefty puzzle:

65 percent of his pitches vs. lefties are going in zones where he gets whiffs at a 25% or better rate. In fact, 49% are going in zones where he’s 39% whiff rate or better. He’s giving up some loud contact when he climbs the ladder away against lefties, but he’s also racking up tremendous whiff rates up there. And that explains why it was one of his most attacked zones vs. lefties, even with a louder exit velocity.

What Makes Jack Flaherty so Special?

To answer the original question, you have to look to the little things. Sure, his stuff is fine, but it doesn’t imply this kind of dominance on the surface level. It’s only once you augment his velocity and spin that the burgeoning ace arrives. His smooth, repeatable mechanics allow him to tunnel his pitches, making him a nightmare with no platoon disadvantage. Tunneling is a huge reason his slider has become such a soul-crushing monster. His deep repertoire, possibly about to get deeper with an enhanced changeup, wreaks havoc on hitters. Finally, if you think you can get him on mistakes, it’s probably not going to happen in a location where you can do much with the pitch. It’s all perfectly refined and amazing to watch, like seeing Bergman direct, Van Gogh paint, or Joey Chestnut eating 74 hot dogs.