The business world is about checking and adjusting. One can concoct a foolproof project plan and have to alter it drastically on day one to accommodate for circumstantial changes. The sports world is no different.
Zach Plesac was called up to make an emergency start in May. He delivered through a rain delay in Boston, posting an impressive 5.1 innings while only allowing one run. That version of Zach Plesac, which was heavily reliant on fastballs and without a slider, is history.
Plesac has continuously adjusted his arsenal, likely with the assistance of Indians catchers Roberto Perez and Kevin Plawecki and pitching coach Carl Willis. He has utilized the data available to work towards leveraging his strengths and managing his weaknesses. A quick glance at his pitch usage shifts reveals a trend that cannot be ignored.
The fastball trend line is the most glaring. He has diverted his attention away from it to attribute to other pitches. The why is simple: While it has an appropriate dose of speed, averaging around 94 miles per hour, it is fairly straight and relies on being located perfectly. This results in allowing a hitter-friendly weighted on base average of 0.368 thanks to an average exit velocity against of 93.3 miles per hour. The approximate 15% shift away from it over the summer is a direct result of checking and adjusting.
Plesac has changed those fastballs out for sliders. Used as a last resort in his first start in the bigs in Boston, the slide piece has turned into his best friend. His reliance on it has shifted, surpassing 20% of his total pitches levels. His swinging strike rates have gleaned the benefits. Though they haven’t made extreme headway to this point, the positive trend line infers a possible relationship with its usage.
If Plesac is going to make the next requisite jump to becoming a projectable starter, the development of this slider is imperative. As with his fastball being a danger because of its weighted on base average allowed, the opposite is true for the slider. Plesac’s sliders have permitted just a 0.281 wOBA, nearly 100 points lower than his fastballs and the difference between well below league average and well above.
Check. Adjust. Check. Adjust some more.
The raw whiff percentages are even more revealing as to why he’s trusting his slider more and more. Over all of his starts, which are plotted in the above graphic, it has transformed into a dependable source for swings and misses. The development is even more apparent over his last three outings. It is trending towards success.
Another positive trend line jumps out given that whiff percentage graphic — the changeup. Billed as his go-to pitch throughout his minor league tenure, early returns were less than stellar. Of late, however, the changeup has developed into a weapon.
The changeup factors in as a contact mitigation tool. It has achieved an impressive 0.242 opponent wOBA while reducing hitters to weak contact (average exit velocity against of 85.7 miles per hour). The gap between his dynamite ERA and poor FIP outputs is told in these contact management ventures with his sliders and changeups.
Diversion from living and dying by his fastball was somewhat expected given the Indians history of it at the major league level. Corey Kluber, Carlos Carrasco, and Trevor Bauer are the landmark cases in this regard. The question becomes what happens next.
Zach Plesac has made the transformation. The result is yet to be determined with favorable early returns on the peripheral spectrum. He has to find a way to leverage increased usage of his slider and changeup into more strikeouts. Whiff percentage will continue to be the barometer… we should not allow ourselves to be swayed by start by start performance. While watching Zach Plesac trek to the mound today against the New York Yankees and y the rest of the season, we must look for swings and misses on changeups and sliders. This will be the Plesac lifeline.
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