Kuhl’s below-average secondaries kept him from prospect relevance. Well, does a .216 xwOBA slider and a .197 xwOBA curveball sound below-average to you? If you’re not sure, from 2017-2018 Kuhl’s curveball ranked 11th best in xwOBA among starters, and his slider ranked 9th, sandwiched right between Sonny Gray and Luis Severino.
This graph depicts every pitcher who threw at least 1,000 breaking balls from 2017 to 2018, with xwOBA of said pitches in the x-axis and pitch usage on the y-axis. As you can see from the other names I highlighted, Kuhl’s breaking balls measure up to some of the best pitchers in all of baseball, as he posted a better xwOBA on his slider/curveball than guys like Max Scherzer, Justin Verlander, Gerrit Cole, and Jacob deGrom. This isn’t a coincidence or luck either; both of Kuhl’s breaking balls grew into elite pitches. His curveball has elite spin-rate, averaging the 16th highest mark in 2018, as well as above-average movement in both directions.
His slider also possesses above-average spin and movement, which while not as high as his curveball, are very impressive for its 88.3 MPH average velocity. Eye test will also confirm that both of these pitches are truly above-average pitches, despite what scouts and the Pirates’ themselves thought about him as a prospect. Kuhl had a curveball coming out of college, but the Pirates pushed him to drop it in favor of a slider when he was in the minors. He didn’t pick it back up again until 2017.
The reason I used pitch usage as my y-axis is to show what the big issue with Chad Kuhl is. Despite having a combined xwOBA of .211, Kuhl only threw his breaking balls for 29.5% of his pitches. Of the pitchers with better breaking balls than Kuhl, only Charlie Morton, Corey Kluber, Blake Snell, and Ivan Nova used them less than him. This is especially concerning when you consider the fact that Kuhl throws both a slider and a curveball, while a large percentage of the pitchers on this chart mainly throw one or the other. It’s worth noting that a few guys in a similar position on the chart to Kuhl, such as Paxton, Morton, and Kluber, have a low percentage of breaking balls because they have a pitch which statcast identifies as a cutter, even though it acts more like a slider (although Paxton and Morton didn’t have significant usage on this pitch).
If you include his Cutter, Kluber’s percentage of breaking balls would jump to 51.6%. That just leaves the other three. Morton and Snell can be explained fairly simply by the fact that they all have plus fastballs, as do most guys with elite breaking balls but low usage, so they don’t need to rely on their breaking balls as much. It’s also worth noting that, like almost every pitcher close in proximity on the chart to Kuhl, Morton increased his percentage significantly in 2019. From 2017-2018, Morton used his curveball and cutter for 37.7% of his pitches. In 2019, that number rose from 47.7%, as he used his curveball especially significantly more, and he had the best season of his career by far. That just leaves Ivan Nova, and to explain that one, all I need to do is tell you to check what team Nova played for from 2017-2018, and the issue starts to become pretty clear.
Going back to the fact that most guys with elite breaking balls and low usage have elite fastballs, or at the very least above-average, let’s talk about Chad Kuhl’s fastball.
So the first thing that stands out (other than the mess in this middle of the graph. That’s Snell, Clevinger, and Strasburg by the way) is just how bad Chad Kuhl’s fastballs were over this period. Despite elite velocity, Kuhl’s .404 xwOBA on these pitches was 3rd worst in the majors over this period, ahead of only Matt Moore and James Shields.
The other obvious thing about this graph is that good pitchers tend to have good fastballs. The only highlighted pitcher with an xwOBA on fastballs over .350 was Patrick Corbin, which is easily explained by his breaking ball percentage of 44.1%. (39.5% slider). This is a pretty simple concept that seems to elude many MLB organizations; pitchers should throw their best pitches more often. I personally think pitchers could throw secondary pitches 100% of the time if their secondaries are good enough and their fastball is that bad, but I won’t try to push those radical beliefs on you guys.
The reason that even guys with fastballs this bad throw them a lot comes down to being able to throw strikes. The concern when raising secondaries is always that BB% will rise, which is true, but if K% rises enough as well, then it’s a worthwhile move because strikeouts are worth much more in the positive direction than walks are in the negative direction. Contrary to popular belief, adding 10 points to your K%+ while also adding 10 points to your BB%+ would actually be a huge improvement for a pitcher. The key here is finding a balance, which Chad Kuhl clearly hasn’t done, and something that the Pirates barely tried to do under Ray Searage.
The natural question here would be “how good can a pitcher be with a really bad fastball?”. Well in this sample size alone, there’s a pretty good answer, and his name is Carlos Carrasco. Of all pitchers who threw 2,500 fastballs from 2017 to 2018, Carrasco ranked sixth-worst in xwOBA at .393, just three spots ahead of Kuhl himself. Over the same time period, Carrasco posted 10.4 fWAR (7th highest in baseball) to go along with a 3.04 FIP across 386.2 IP. In the same sample, Patrick Corbin ranked 25th worst in fastball xwOBA at .364, and it got even worse in 2019. That didn’t keep Corbin from accumulating 13.9 fWAR over the last three years (7th highest in baseball). Marcus Stroman and Luis Castillo ranked 20th and 16th worst in fastball xwOBA over the same period, but still managed to put up 4.8 fWAR and 4.0 fWAR respectively. I think you get the point.
Do I think Chad Kuhl can be as good as these guys? Actually, yes. Yes I do.
* I can't figure out how to make the graphs larger on this board... Someone able to help?