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Going back to the start of the 2018 season, there is one pitcher in all of MLB who’s in the top 10 in ERA, WHIP, FIP, walk rate and strikeout rate minus walk rate. Care to make any guesses?

Jacob deGrom? Nope. He’s one of four pitchers to come up short in only walk rate, along with Chris Sale, Max Scherzer and Blake Snell. How about Justin Verlander? He, too, checks four of the five boxes, subbing in walk rate for FIP. Clayton Kershaw and Gerrit Cole both hit three, while Trevor Bauer and Patrick Corbin are included in two, but just one starter finds himself among all five top 10s from the start of last year through Friday. His name?

Hyun-jin Ryu.

Over the last two seasons, Ryu is 12-4, with a 1.87 ERA, 0.90 WHIP, 2.89 FIP and 143 strikeouts against 18 walks in 134 2/3 innings. His strikeout rate is 27.9% and his walk rate is 3.5%, good for a difference of 24.4%. That makes him first in ERA and walk rate, second in WHIP, seventh in FIP, and eighth in strikeout rate minus walk rate since the start of the 2018 campaign. That’s quite an unlikely pitcher to be the only one in the top 10 in all five categories.


To be clear, I moved the goalposts a bit on this one. Ryu pitched just 82 1/3 innings last year while spending about three months on the IL with a groin injury. He didn’t throw enough innings last year to qualify for the ERA title, so you won’t see him on traditional leaderboards. Still, by combining the last two seasons, we get him to a sample of 134 2/3 innings and 23 starts. That’s nearly a typical full season, across which Ryu has been one of the very best starters in the majors, a true ace, full stop. That’s worthy of a deeper look.

The biggest change Ryu made in advance of 2018 was committing a significant share of his pitch mix to his cutter. He debuted the pitch in 2017, throwing it 17.8% of the time. The cutter’s usage rate rose to 24.5% last year, and sits at 21.2% this season. At the same time, he ditched his slider and cut back on his four-seam fastball, going from a 52.4% usage rate in 2014, his last season before losing two full years to a shoulder injury, to 36.9% in 2017, and 29.7% this year.

Of course, Ryu’s still got the changeup that has always been his go-to out-pitch and remains at the center of his repertoire. He threw it 17.7% of the time last year, and has upped that to 23.4% this year. It has a whiff rate of 20.4%, and 16 of his 54 strike threes have come with the change. Hitters are managing just a .121 batting average and .207 slugging percentage against it, with righties struggling to the tune of a .175 slugging percentage. Take a look at it in all its glory.

It’s the cutter, however, that deserves our focus. After all, that’s the pitch that has taken on greater importance in Ryu’s ascent to ace status over the last two years. It registers at a touch better than 87 mph on the radar gun, about three mph slower than his four-seamer. Hitters do have six homers against it going back to the start of last season, but have hit just .245 against it as an action pitch. That doesn’t include all the whiffs in zero-strike and one-strike counts.

Ryu’s cutter has been even better this year than it was last year, a fact made clear by a doubling in whiff rate to 15.9% from 7.7%. As the two GIFs above might indicate, command and control of the pitch has been key for Ryu this season. Below are Ryu’s heatmaps for his cutter over the last two seasons. The first is from 2019, and the second is from 2018. These heatmaps, courtesy of Statcast, are from the catcher’s perspective.


Notice how this season he has been living off the plate inside to righties and away from lefties, while last year he was in the zone with the pitch far more often? That has led to more whiffs and weak contact. Ryu’s cutter has a chase rate of 16.5% this year. Last year, that was down at 6.2%.

There’s reason to believe a mechanical change is behind Ryu’s ability to hit that intended spot with more regularity this season. Check out Ryu’s plot of release points for each cutter thrown over the last two seasons. Again, the first one is from this year, and the second one is from last year.


Ryu is releasing his cutter higher and a bit farther away from his body this year than he did last year. Is that a surefire formula for improved command of a specific pitch? Honestly, I don’t have a concrete answer for that question. What we can say, though, is that it is a substantive mechanical change, and that Ryu has been better with the pitch this season. Correlation doesn’t equal causation, but the change is significant enough that it could be behind the pitch’s improved effectiveness.

What we know for sure is that the cutter has given Ryu a second out-pitch, and that he has been among the best pitchers in the league since pairing it with his changeup last year. Injury concerns with him are ever-present, more so than the average pitcher, but when he’s healthy we should trust him as a legitimate ace.