Jack Flaherty Has Become the Most Dominant Pitcher in the National League

Ever since they were swept in Oakland and LA near the beginning of August, the Cardinals have been on fire! How have they fueled this latest surge? With around average to below-average stats in all the offensive categories over the last month (21st in batting average, 24th in slugging), the answer is pitching and defense. Aside from Harrison Bader, they don’t have anyone who will make the flashy plays, but they make very few mistakes. They have the fewest errors in the majors at only 59. Seven less than anyone else, 23 less errors than the Brewers and 40 less than the Cubs. A string of really solid starters and a bullpen with the 2nd lowest ERA in the MLB over the last month has fueled this latest run for the NL Central division title. The image below shows the rolling ERA of each of the Cardinals’ starters throughout the season.


Dakota Hudson is one of the hot arms the Cardinals have been riding. Despite a low strikeout rate, Hudson’s success has come heavily because of his high-ground ball rate and the Cardinals’ solid defense. Adam Wainwright has been very strong recently and Michael Wacha started the season terribly and has been just okay since. Miles Mikolas hasn’t been as good as he was last season, but he has been better lately, allowing three or less runs in each of his last three starts. But the one pitcher completely dominating opponents, is Jack Flaherty.

Flaherty’s earned runs in his outings since the break read: 1, 0, 2, 0, 0, 0, 1, 0, 2, 0 and 0. His ERA since the break is a league-leading 0.82. The next best on the list is Sonny Gray at 1.61. Almost an entire run better than anyone else! He has allowed the lowest batting average and slugging percentage among qualified pitchers since the All-Star break. Below are the top pitchers in the MLB in batting average allowed since the break.


The key to Flaherty’s success has been his fastball. In terms of pitch value (how well a pitcher performed using a certain pitch), Flaherty’s fastball has been the best among all starting pitchers in the MLB since the break. That doesn’t mean it’s the fastest, it just means it has been more effective than any other pitcher’s fastball. The table below shows the best pitchers in fastball pitch value since the All-Star break.

Rank Name Team Fastball Value Slider Value
1 Jack Flaherty Cardinals 2.76 3.41
2 Gerrit Cole Astros 2.25 2.08
3 Julio Teheran Braves 1.98 -1.79
4 Chris Bassitt Athletics 1.89 -5.52
5 Jacob deGrom Mets 1.74 1.60
6 Shane Bieber Indians 1.59 2.38
7 Lucas Giolito White Sox 1.45 -1.59
8 Justin Verlander Astros 1.43 4.29
9 Adrian Houser Brewers 1.40 -1.43
10 Mike Clevinger Indians 1.35 2.04

The fastball isn’t the only thing making Flaherty more dominant. It’s his slider too, ranking 4th in the MLB in pitch value, behind only Justin Verlander, Ryan Yarbrough and Noah Syndergaard. In terms of just usage, Flaherty is throwing slider about 5% more since the break and fastball up about 1%.

Let’s look at why they might all of a sudden be so effective. My thought is simple: location. I’ll use heat maps to illustrate what I mean. The first heat map shows where Flaherty threw his fastballs in the first half of 2019. The second shows where he’s thrown them in the second half of 2019 (All heat maps are from catcher’s perspective).

Fastballs Before All-Star Break vs. Fastballs After All-Star Break

There is a HUGE difference between where he’s throwing his fastballs. The first half shows the much redder areas at the top of the zone, while the second half heat map shows Flaherty throwing heavily at the bottom of the zone. Okay, so he’s throwing his fastballs lower, but why would throwing fastballs at the bottom of the zone make Flaherty so deadly? To answer that we need to look at the heat map of Flaherty’s sliders. The heat maps below show Flaherty’s sliders before and after the All-Star break.

Sliders Before All-Star Break vs. Sliders After All-Star Break


What we see in Flaherty’s slider heat map is that he throws them low (like every pitcher does), but also he’s throwing them more down the middle and a bit higher than he was before. The key to Flaherty’s success isn’t just one pitch, but how he has been able to use these pitches to work off one another. He accomplishes this by throwing the fastball lower and bringing his slider up a bit, essentially throwing them on the same plane. Throwing the fastball lower puts the ball on the same plane as his slider as it comes toward the hitter; making it almost impossible to distinguish whether it’s a fastball or a slider until it’s too late. Flaherty has created deception and it’s propelled him into a true Ace of the rotation.

Pitchers don’t just go from struggling in the first half to becoming the best starter in baseball; there’s always a reason. Flaherty is locating his pitches, fooling hitters with deception and inducing weak contact. The Cardinals haven’t been scoring too much lately, but if Flaherty keeps this up, they may not have to.



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