Setting Reasonable Expectations for Kohei Arihara

On Christmas, while I was some combination of calorically comatose and consumed by basketball, Ken Rosenthal of The Athletic reported that the Rangers had signed 28-year-old Japanese righty Kohei Arihara. The move continued an active Texas offseason and streak of curious, perhaps antithetical acquisitions made by a Rangers club that seems to have one foot in rebuilding and and the other in competing. What does Arihara bring to the table right now, and how does his acquisition fit as part of a broader shift in the strategy the org seems to be taking to team building?

Before I talk about Arihara, let’s remember the things that change when a pitcher goes from NPB (Nippon Professional Baseball) to MLB. In addition to the leap in hitter quality, there is also a heavier workload. Pacific League pitchers start once a week rather than once every five days as they typically do in MLB. It’s a strange cultural workload reversal from high school, where Japanese pitchers can be sometimes driven into the ground and asked to throw upwards of 120 pitches on little rest during important tournaments. There’s no way of knowing what kind of long-term consequences this has for the pitchers being developed there, good or bad.

The baseball itself is also different. The tackiness and seam height of NPB’s ball differs from MLB’s (there’s also variance within each population on its own), and those attributes play an important role in creating movement on pitches. This is why, more and more often, you’ll see MLB pitchers asking the umpire for a new baseball after feeling the seams on the one they’ve just been given and realizing they are lower than they like. All of these things, in addition to the complexities of a cross-planet move and cultural adjustment, play a role in augmenting teams’ understanding of the pitchers they have scouted, via tech and eyeball evaluators, in NPB or any other foreign league.

Arihara was the third overall pick in the 2014 NPB draft (out of college), debuted the following year, and spent the next six seasons as a rotation stalwart for the Hokkaido Fighters before he was posted this offseason. After striking out roughly 17% of opposing hitters in his first four pro years, he had a modest velocity spike and subsequent uptick in strikeout rate (25%) in 2019, then continued to throw harder still in 2020 (his fastball was averaged 92 mph this season) though his strikeout rate of around 19% regressed closer to, but was still above, his previous career norms.

Kohei Arihara Fastball Velocity by Year
Year Fastball Velo K% SwingingStr%
2015 90.6 17.9% 9.1%
2016 90.9 16.1% 8.3%
2017 91.2 12.2% 8.8%
2018 91.2 18.5% 9.9%
2019 91.7 25.2% 13.1%
2020 92.1 19.4% 10.5%
The swinging strike rate is for all pitches, not just fastballs.

His strikeout uptick coincided with reduced usage of his four-seamer and increased use of both his sinker and changeup, and his splitter and change (DeltaGraphs lists him as using both) are the best of his many pitches. Though you’ll occasionally see Arihara toss in a lollipop curveball around 70 mph, he more evenly mixes a four-seamer, sinker, slider, cutter, and the two offspeed pitches. Sometimes he’ll release his splitter in such a way that its movement looks more like a slider than a split. The result is a very deep repertoire of modest quality, pitches that, aside from the change of pace stuff, rely on location to get outs rather than pure stuff. But Arihara does throw plenty of strikes: He has had one of the 10-lowest walk rates among qualified starters in NPB four of the last five years.

It’s just a theory, but I’d be more comfortable signing NPB pitchers whose out-pitch is a split or a change rather than a breaking ball. I think the characteristics of the NPB ball make it easier than the MLB ball to spin, so there’s increased risk that a slider or curveball that looks nasty in NPB is diluted by the MLB ball. As a crude test of this, I averaged the three-year pre- and post-MLB FIP of the recent Japanese pitchers and gave each of them a primary out pitch classification to see if breaking ball guys’ performance took more of a hit in MLB.

Former NPB Pitchers Performance
Pitcher Fastball Velo Splitter or Slider? Final 3yr NPB FIP First 3yr MLB FIP Delta
Daisuke Matsuzaka 91.9 Slider 3.01 4.45 -1.44
Yu Darvish 92.8 Slider 1.98 3.13 -1.15
Yusei Kikuchi 93 Slider 3.34 5.17 -1.83
Hiroki Kuroda 92 Slider 3.66 3.48 0.18
Masahiro Tanaka 91.5 Even Mix 2.01 3.51 -1.5
Kyuji Fujikawa 91.4 Splitter 2.04 4.11 -2.07
Hisashi Iwakuma 89 Splitter 3.47 3.68 -0.21
Yoshi Hirano 91.2 Splitter 3.39 4.02 -0.63
Koji Uehara 88 Splitter 3.32 3.00 0.32

It’s a small sample of players, but I’ll note the splitter group is about half a run better than the slider guys when headed to MLB compared to previous performance, and the gap would be bigger if it weren’t for Hiroki Kuroda, who eventually leaned on a splitter later in his career but was slider-dependent early on.

Keep in mind that Arihara threw 132 innings in 2020, nearly 50 innings more than Lance Lynn, who led 2020 MLB with 85. As literally every MLB pitcher may be asked to deal with the biggest year-to-year innings increase of their careers, that Arihara is coming off a longer season may be advantageous for his stamina relative to his new peers.

I’ve added Arihara to the International Players tab over on The Board and he’ll eventually be on the Rangers prospect list when it is published later this offseason. He’s a 40 FV player for me, someone who I think can be plugged right into the back of a rotation and work as a 1.0 to 1.5 WAR starting pitcher. (There are some folks in baseball who think he’ll be a little better than I do, but I can’t find anyone who thinks he’ll be this good, and I bet if you can figure out what all four players in these tweets have in common that you’ll have a good idea of who the “evaluator” referenced here is.) His deal is for two years, $3.6 million in 2021 and $2.6 million in 2022, plus some performance incentives and the $1.2 million posting fee. It means Texas’ total outlay is just north of $7 million over two years, which is commensurate with the evaluation I have on Arihara.

Eric Longenhagen is from Catasauqua, PA and currently lives in Tempe, AZ. He spent four years working for the Phillies Triple-A affiliate, two with Baseball Info Solutions and two contributing to prospect coverage at Previous work can also be found at Sports On Earth, CrashburnAlley and Prospect Insider.

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3 years ago

Arihara reminds me a lot of Mike Leake with more velocity.