Forecasting Shun Yamaguchi’s impact on Blue Jays’ pitching staff

Shun Yamaguchi. (Toru Takahashi/AP)

If there’s one thing the Toronto Blue Jays have accomplished this off-season, it’s successfully stocking their rotation with known quantities.

Despite their supply of MLB-ready youngsters like Ryan Borucki, Trent Thornton, Anthony Kay, Jacob Waguespack, and T.J. Zeuch, this front office determined that the time for leaning exclusively on those inexperienced arms was over. In came Hyun-Jin Ryu and Tanner Roark via free agency, Chase Anderson via trade, plus the return of Matt Shoemaker.

While Ryu and Shoemaker in particular come with health questions, you at least know what you’re going to get from any of those four when they’re on the mound, which is more than can be said for the team’s other arms — perhaps with the eventual exception of Nate Pearson.

Amidst these moves, the Blue Jays added one pitcher who doesn’t remotely fit that description by inking Shun Yamaguchi to a two-year $6.35 million deal. Of all the pitchers the Blue Jays added, the 32-year-old right-hander comes with the widest range of outcomes. He could be an absolute bargain, a total bust, or anything in between.

What we can say with confidence is that he brings a track record of success in Japan. He’s got 1093.1 NPB innings under his belt and in 2019 he led the league in strikeouts while pitching 181 innings of 2.78 ERA ball. The uncertainty is whether his stuff will hold up at the highest level, especially enough to justify the rotation spot he’ll be fighting for in the spring.

Really, that’s a two part question:

1. What does Yamaguchi’s arsenal look like?
2. How do pitchers with a similar arsenal fare in the majors?

The first question can be answered by Deltagraphs – the Japanese equivalent of FanGraphs – as decoded by veteran Japanese baseball journalist Jim Allen. Last season Yamaguchi’s pitch breakdown looked like this:

Pitch Usage
Fastball 43.70%
Splitter 26.60%
Slider 20.20%
Curveball 8.20%
Sinker 1.20%

Another crucial piece of information for understanding Yamaguchi’s arsenal is his velocity. In 2019, he averaged approximately 90.1 m.p.h. with his fastball.

That’s enough information to help us understand the basics of what the right-hander brings to the table. In an ideal world it would be nice to know some horizontal and vertical movement scores and spin rates, but this is still a start — enough to help us find similar pitchers to Yamaguchi.

In order to pinpoint those players, and answer our second question, I looked at pitcher seasons that met the following criteria:

1. At least 100 innings pitched.
Although Yamaguchi could easily be used as a reliever — and he actually pitched exclusively out of the bullpen in Japan from 2008-2013 — he’s going to get a chance to try his hand at starting. Whether he wins the fifth rotation spot outright or someone gets injured in front of him, his chances of opening the season as a starter seem pretty good. Another important aspect of this stipulation is that it provides a decent minimum sample size. There’s often not too much to be learned from individual reliever seasons.

2. Fastball velocity between 88-92 m.p.h.
It’s hard to consider the arsenals of two different pitchers similar if they have extremely different velocities. For instance, Nathan Eovaldi’s 2016 season met all of the other criteria on this list, but considering he threw an average fastball at 97 m.p.h. that year it’s hard to imagine his success telling us much about what Yamaguchi will do at approximately 90 m.p.h.

3. Fastball usage under 50 per cent.
One of the things that stands out most about Yamaguchi’s pitch usage numbers is how little he uses his fastball. Even as fastball rates are plunging league-wide, only 18 of the 130 pitchers who managed 100 innings last year threw their heater as infrequently as Yamaguchi did in Japan.

4. Splitter usage of 20 per cent or higher.
Yamaguchi’s splitter is his top swing-and-miss pitch and his most-used secondary offering. It’s also a relatively rare pitch in modern baseball. For instance, only four of the aforementioned 130 pitchers from 2019 meet this criteria.

Since 2002, when FanGraphs began tracking pitch usage, there have been 2,547 pitcher seasons with at least 100 innings and only 14 of those seasons meet all the criteria above.

Pitcher Season
Jose Contreras 2008
Braden Looper 2009
Carlos Zambrano 2012
Hiroki Kuroda 2013, 2014
Hisashi Iwakuma 2014, 2015
Masahiro Tanaka 2014, 2015, 2016, 2018, 2019
Miguel Gonzalez 2016
Matt Shoemaker 2016

It’s interesting to note that nine of these 14 seasons were delivered by Japanese pitchers. Comparisons based on cultural backgrounds are often lazy, but it’s clear Yamaguchi’s style is similar to peers with NPB experience. Japanese imports often come equipped with splitters and rarely wield elite velocity.

The best season on that list by WAR is Masahiro Tanaka’s 2016 which comes in at a near-elite 4.7. The worst is Braden Looper’s disastrous 2009, which was the last season of his career. Looper threw 194.2 innings of 5.22 ERA ball while leading the league in home runs (39) and earned runs allowed (113) and posting a -0.5 WAR.

The average of these seasons look like this:

Players Age K/9 BB/9 HR/9 ERA WAR/100 IP
Yamaguchi comps 31.8 7.17 2.04 1.11 3.82 1.5

That’s the type of production the Blue Jays would undoubtedly be happy with from Yamaguchi, but the numbers here are a bit skewed. Tanaka’s stats play heavily into them and he may not be a fair comp considering he was much younger than Yamaguchi is now when he posted most of these statistics, his velocity tends towards the highest end of the 88-92 m.p.h. range, and his best weapon is probably his slider not his splitter (although both are deadly).

If we remove Tanaka’s seasons, we’re left with a more reasonable expectation for Yamaguchi:

Players Age K/9 BB/9 HR/9 ERA WAR/100 IP
Non-Tanaka comps 35.3 6.59 2.22 1.03 3.98 1.3

It seems that what Yamaguchi brings to the table is the repertoire of a crafty older pitcher who doesn’t miss many bats, but commands the ball well and limits damage. Based on his track record in Japan, it’s probably safe to assume the Blue Jays righty would strike out and walk more hitters than this — and a higher HR/9 is a smart bet given the surging home run rate around the league.

That said, Toronto would be ecstatic to get similar production to this from Yamaguchi based on what they’re paying him. Even if he maintained these rates exclusively out the bullpen he’d be a good value.

Even though MLB pitchers similar to Yamaguchi are very rare, there’s a clear precedent of them finding success. They haven’t succeeded on the strength of their stuff alone, though. It seems they’re generally older pitchers with diminished velocity using command and guile to get by. Before long, we’ll see whether Yamaguchi has enough of those qualities to thrive in the majors, too.

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