Which Yankees pitchers changed the most in 2018?

Earlier this week, I highlighted the Yankees hitters that changed the most in 2018. In particular, I looked at Gleyber Torres, who transformed into a power hitter upon reaching majors, and Giancarlo Stanton, who looked like he might’ve been trying to do too much at times in his first year in pinstripes.

Let’s look now at the pitchers who changed the most this season. To reiterate, we’re not necessarily looking for players whose performance changed the most. Sonny Gray’s level of play changed drastically from 2017 to 2018, but the shape of his play didn’t change noticeably. He just played worse. We’re looking for players whose process changed, regardless of result.

Masahiro Tanaka

Tanaka may not seem like an obvious candidate for this list. He has always been known as a sort of “pitch backwards” type, and that was no different in 2018. The extent to which Tanaka committed to the pitching backwards philosophy changed in 2018.

In fully embracing his reliance on his best, secondary pitches, his slider and splitter, Tanaka actually morphed himself into a three-pitch pitcher. As recently as 2017, Tanaka was a legitimate six-pitcher hurler. According to Statcast, Tanaka used six pitches, his aforementioned secondaries, his four-seam, two-seam, and cut fastballs, and a curveball, at least five percent of the time.

In 2018, Tanaka was, for all intents and purposes, a four-seam, slider, and splitter guy. He used his four-seamer 22 percent of the time, more than four times as much as his next most-used fastball. He used his splitter 31 percent of the time, and his slider 33 percent of the time. He almost completely forsake his curve and his cutter, throwing each maybe a couple times per start. Tanaka also vastly cut his sinker usage, dropping it from 18 percent to 5 percent.

This is a bit surprising to see from a pitcher that was lauded for his deep, diverse arsenal when he entered the league. He would turn over lineups multiple times with several different pitches, never relying on one or two offerings too much. Now, Tanaka has zeroed in on what he presumably feels are his best pitches. He also seems to have subscribed to modern pitching orthodoxy, attacking with four-seamers up in the zone and breaking pitches below the zone.

Pitching to contact with sinkers and cutters, and dropping in slow curves, has become passe for Tanaka. For the most part, this looks like a good idea. Opponents brutalized Tanaka’s sinker, previously his highest-usage fastball, to the tune of a .340 average and .641 slugging in 2017. This year, hitters posted wOBA figures of .250 and .252 against his slider and splitter, respectively.

While it goes against the kind of pitcher he was when he was younger, culling his repertoire to focus on his best pitches is smart. It’s probably not a coincidence that Tanaka significantly cut both is adjusted ERA and FIP marks from 2017 to 2018. Hopefully, this three-pitch version of Tanaka will be the best version going forward.

Tommy Kahnle

Kahnle is a more obvious entry. You could watch a Tanaka start and perhaps not notice that he had suddenly turned into a three-pitch pitcher. You couldn’t really watch Kahnle pitch and not see what had changed with him.

Of course, Kahnle completely lost his velocity in 2018, and it cost him. This chart, courtesy of Brooks Baseball, is telling:

Kahnle’s velocity increased in 2017, and he had a breakout year. He completely lost those gains early in 2018, and he never recovered. After averaging over 98 mph on his fastball in 2017, Kahnle averaged 95 mph in 2018.

Losing two or three ticks of fastball velocity in one year is nearly impossible to overcome. Last season, opposing hitters posted a .271 wOBA against Kahnle’s four-seamer, an outstanding figure for a fastball. This year, they crushed it for a .495 wOBA. Kahnle’s primary offspeed pitch, his changeup, still performed well, holding hitters to just four hits in 38 at-bats. Kahnle’s decline was almost entirely attributable to his fastball’s pitiful performance.

Kahnle did spend plenty of time on the disabled list in 2018, but even after returning to health, he was unable to find his lost velocity. He struggled upon coming back to the majors in August, and ultimately gave up 22 runs in 23.1 innings on the year. This, after posting a 171 ERA+ in 2017, striking out 96 batters in 62.2 innings.

A big reason the Yankees traded for Kahnle last year was the fact that he won’t reach free agency until after 2020. He figured to be a prominent part of the Yankees’ bullpen for years to come. After such a sudden and devastating velocity loss, there’s no telling what comes next for Kahnle. With the Yankees potentially losing multiple high-end relief arms over the next couple winters, Kahnle’s disappearance could prove costly.