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Dissecting Jack Flaherty’s Approach Against Lefties

In 2018, Jack Flaherty took significant strides towards looking like a potential front-of-the-rotation starter for the St. Louis Cardinals. He posted a 3.34 ERA across 151 innings, striking out nearly 30% of the batters he faced, while holding a 3.58 xFIP. Additionally, he maintained strong numbers against both righties and lefties. As a result, expectations for Flaherty in 2019 were high. Projection systems called for an ERA between 3.30 and 3.60, which placed Flaherty among the top 15-20 pitchers in baseball, depending on the algorithm. However, through 97 innings in 2019, Flaherty has fallen short of those marks. Going into the All-Star break, the young righty held a 4.64 ERA with a 4.07 xFIP. Peripherally, his strikeout rate (K%) is down 3%, his ground-ball rate (GB%) is down 5%, and his hard-hit% is up as well. Investigating further, one of the biggest differences between Flaherty’s 2018 and 2019 seasons is his performance against left-handed hitters.


While worse than his performance against righties, in Flaherty’s .275 wOBA against left-handed hitters in 2018 ranked eighth out of all right-handed pitchers with more than 300 total lefties faced, and his 26.8% strikeout rate against them ranked twelfth. Those numbers place him around pitchers like Aaron Nola, Jose Berrios, and the 2018 version of Mike Foltynewicz. Those are good pitchers! However, Flaherty’s performance against lefties in 2019 has not held up — take a look at the numbers.


It’s easy to see, but through the first half of the 2019 season, Flaherty has been drastically less productive. His surrounding numbers paint the whole picture: the average exit velocity from lefties has risen from 81.9 mph to 84.4 mph, with their GB% dropping from 42.5% to 35.8%. Lefties have been replacing those ground balls with batted balls in the air, as his FB% went from 34.4% to 41.8%. It doesn’t help either that his HR/FB rate has nearly doubled across the two seasons. The bottom line is that lefties are hitting him harder, and when they do so, their results are better. Read the rest of this entry »