Author Archive

Fixing Zack Wheeler’s Fastball Mix

Although he may not have been one of truly few elite free agents on the market, Zack Wheeler was a very big signing for Philadelphia, agreeing to a five-year contract worth $118 million. Over the past two years, Wheeler’s amassed an fWAR of 8.9 in 377.2 innings while posting above-average strikeout and walk rates. Additionally, his underlying metrics have also been strong over the past two seasons, and they don’t signal any drastic mean reversals in performance. Granted, there is obviously still risk here. Wheeler missed the 2015 season and the start of 2016 with a UCL tear, and he was shut down upon his return with a flexor strain. Furthermore, this past July he was shut down with shoulder fatigue, limiting the Mets’ ability to market him to potential suitors at the trade deadline.

One of the most interesting storylines in the game is player development. At the moment, the most analytically inclined teams are thriving at meshing the data with coaching, and the gap is only growing. These teams are creating new players. This is particularly important when signing free agents given the current contract negotiation dynamics. The teams and players have access to most of the same information, with the $/WAR metric playing a central role in future valuations, and if you can “create” a new player who beats the projections, you’re generating additional value for your club.

In terms of Wheeler, I think I have a bit of a theory on how to generate that marginal value through a tweak in his approach. The biggest change in Wheeler’s approach between 2018 and 2019 was in his usage of his fastballs and his changeup. In 2018, the righty threw his four-seam fastball almost three times as frequently as his two-seamer, and his changeup was almost almost non-existent. (Disclaimer: I believe that there may be an error in Statcasts’ classification of Wheeler’s splitter and changeup — they may actually be the same pitch). Read the rest of this entry »

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 »