Yusei Kukuchi Mariners

The rebuilding Seattle Mariners are flirting with playoff contention in late-August, which was totally unexpected. The odds don’t favor the Mariners. But a late-season rebound by All-Star Yusei Kikuchi is essential to the team having any chance of pulling off a September surprise.

Since the Midsummer Classic, Kikuchi hasn’t performed like an All-Star with a 6.46 ERA in eight starts and opponents hitting .298 against him. So, what’s gone wrong with his All-Star season?

A lot, recently.

Meh, All-Star, And Yikes!

Kikuchi’s season can be broken into three distinct phases. The first encompasses his initial four starts, which could be described as “meh.” During this span, he was inconsistent and often hit hard. So much so, some Mariners fans were questioning whether the left-hander would ever become a standout starter for the team.

The Three Phases of Kikuchi's 2021 Season
Phase
G
ERA
AVG
wOBA
HR%
BB%
K%
Apr 2-23
4
5.70
.253
.329
4.9
8.9
19.8
Apr 29 - Jul 1
11
2.33
.173
.249
3.8
8.3
27.5
Jul 7 - Aug 26
9
6.75
.304
.406
5.3
9.6
25.0

What followed next was the fun phase, an 11-game span that began with a strong outing against the Astros on April 29 and continued through July 1. For just over two months, Kikuchi was among the best pitchers in baseball. This stretch is why he earned his first All-Star selection.

That brings us to the current phase – Kikuchi’s nine starts after his July 1 outing. This period has fans saying “yikes,” among other things. It’s also the impetus for this piece – my third about the native of Japan since last season.

So, what’s changed since Kikuchi’s best phase of the season?

Again, the answer is a lot.

Diminished Fastball Velocity

Mariners manager Scott Servais has stressed during the season that Kikuchi establishing his four-seam fastball early in games was paramount to his success. Servais’ sentiment resonates once we notice how the 30-year-old’s average four-seam velocity peaked during the All-Star phase of his season.

Kikuchi's Average Four-Seam Fastball Velocity (MPH)
2021
Apr 2-23
Apr 29 - Jul 1
Jul 7 - Aug 26
95.3
94.7
96.1
94.5

Is Kikuchi’s recent drop in fastball velocity cause for concern?

On the surface, the answer may appear to be no. After all, we’re a talking about a decline of 1.6 MPH between April-July and now. Then again, when we look at how often Kikuchi’s fastball has cracked the 95 MPH barrier during the different phases of the season, we discover something worth discussing.

The following illustrates how frequently Kikuchi four-seam fastballs were 95 MPH or greater in games. Also included, the regularity that his four-seamers reached or exceeded 95 MPH in the first inning. Remember Servais’ emphasis on flashing a quality fastball early.

Why Kikuchi is reaching 95 MPH less often is unclear. But the numbers suggest the effectiveness of his four-seamer has diminished along with its velocity since June. Ironically, he’s thrown the pitch more frequently during his recent rough patch than when he was building his All-Star résumé.

Kikuchi's Varying Fastball Success
Pitch %
K%
BB%
AVG
(MPH)
Apr 29 - Jul 1
30.7
40.0
4.0
.125
96.1
Jul 7 - Aug 26
37.9
29.5
13.1
.294
94.6

During Kikuchi’s All-Star surge, the opponent AVG and strikeout rate on his four-seam fastball were third best among 80 pitchers throwing 300-plus four-seamers. Conversely, hitters have a .294 AVG against him ever since, which is 16th highest within his peer group.

Trouble With The Cutter?

Obviously, Kikuchi throwing more four-seamers since early July means he’s altered the frequency of other pitches. Although there have been more changeups and fewer sliders lately, the most dramatic development has been cut-fastball usage – a 13.8% decline since July 7.

Kikuchi's Cutter Usage
4-Seamer
Change
Cutter
Slider
Apr 29 - Jul 1
30.7
9.6
41.4
18.2
Jul 7 - Aug 26
37.9
13.2
27.6
21.2

As with the drop in fastball velocity, the sudden aversion to the cut fastball is unclear to this dopey blogger. That said, a review of Kikuchi’s stats underscores the important result his cutter often produces – ground balls.

This season, the league is hitting .239 and slugging .264 on ground balls. Kikuchi’s success with grounders is even better – .179 AVG and .200 SLG. As you probably expected by now, his ground ball rate has waxed and waned throughout the season.

Kikuchi's Ground Ball Rates In 2021
Apr 2-23
Apr 29 - Jul 1
Jul 7 - Aug 26
GB%
45.1%
58.8%
44.4%

This is where Kikuchi’s cut-fastball re-enters the picture. His cutter has been a ground ball generator since he first debuted the pitch last season. In fact, it had the highest ground ball rate of any cutter thrown at least 100 times in 2020.

Highest Cutter Ground Ball Rate (2020):
Yusei Kikuchi – 29.1%
Josh Tomlin – 28.8%
Nathan Eovaldi – 25%
Yu Darvish – 19.8%
Corbin Burnes – 17.6%

This season, Kikuchi’s 27% cut-fastball ground ball rate is second best in the majors behind Milwaukee’s Corbin Burnes. Unfortunately, Kikuchi’s cutter has been generating fewer grounders lately.

Kikuchi's Cutter-Generated Ground Ball Rates
Apr 2-23
Apr 29 - Jul 1
Jul 7 - Aug 26
GB Rate
26.8%
31.8%
21.1%
MLB Rnk
3
1
2

While Kikuchi’s 21.1% ground ball rate off the cutter ranks second-best among peers, the 10% reduction from April-June is counterproductive. Especially when you consider opponents are hitting just .148 on cutter-generated grounders during the Japanese hurler’s recent struggles.

Something else to consider regarding the Kikuchi cutter/ground ball dynamic. His teammates have his back when hitters put the ball on the ground.

Seattle defenders have produced 10 outs above average (OAA) when Kikuchi is on the mound. That’s ties him for the second highest OOA accrued behind any pitcher with Houston’s Framber Valdez. Only Adam Wainwright of the Cardinals (20 OOA) can boast better support from his defense.

Again, I can’t tell Kikuchi (or any human) how to improve their four-seam fastball velocity. Nor do I have the knowledge or standing to suggest he simply throw more cutters. But it’s obvious that the success of these two pitches are vital to the lefty’s repertoire and overall productivity.

Falling Spin Rate

Since it’s the year of sticky stuff, we have to discuss spin rate. Especially after Kikuchi’s name appeared in a New York Times article last month discussing individuals with the greatest drop in spin rate since the MLB-mandated inspections of pitchers for foreign substances during games.

The Times piece focused on fastball spin. However, I compiled a table illustrating Kikuchi’s monthly average spin rate for each weapon in his arsenal. There was a decline of at least 200 RPM for each pitch with the change-up (-414 RPM) decreasing most since April.

Kikuchi's Spin Rates Are Down Since Opening Day
Cutter
4-Seam
Slider
Changeup
Apr
2409
2356
2521
1684
May
2379
2275
2441
1696
Jun
2272
2246
2420
1597
Jul
2210
2110
2317
1209
Aug
2180
2128
2311
1270
Delta*
-229
-228
-210
-414
* Delta reflects change from April to August

To be clear, I’m not suggesting Kikuchi’s higher spin rates were the result of applying foreign substances to baseballs. After all, the MLB sticky stuff crackdown began on June 15. He had a 1.37 ERA and held hitters to a .167 AVG in his next three starts after rule enforcement began in earnest. Moreover, his three opponents were postseason contenders – the White Sox, Rays, and Blue Jays.

It’s also worth noting Kikuchi did see some variance in average spin rates in 2019. The deltas weren’t nearly as extreme as this year. Additionally, his change-up actually gained spin during his rookie season.

Kikuchi's Average Spin Rates In 2019
Curve
4-Seam
Slider
Change
Apr
2609
2175
2377
1603
May
2490
2121
2299
1722
Jun
2551
2139
2252
1621
Jul
2477
2040
2168
1878
Aug
2456
2011
2133
1790
Delta*
-153
-164
-244
187
* Delta reflects change from April to August

Is there any relevant correlation between Kikuchi’s declining spin rates in 2019 and 2021? I’m not sure. But I wanted to provide the data for your consumption.

Give Me A Break?

The Mariners began the season with a six-man rotation and continued the practice until late-June. Naturally, I’ve wondered whether the change to a five-man rotation had a negative effect on Kikuchi. It’s one of those questions a nerd like me won’t be able to answer. But we can at least see what the numbers tell us.

I grappled with how to best display the differences between the five- and six-man rotations and finally settled on comparing the average days of rest between starts. Please note, the early-season numbers for Tyler Anderson reflect his time with the Pirates. The second column illustrates his stint with Seattle.

Average Days of Rest Between Starts
April-June
July-August
Marco Gonzales
5.4
4.8
Yusei Kikuchi
5.5
4.8
Chris Flexen
5.7
4.6
Logan Gilbert
5.3
4.6
Tyler Anderson
5.1
4.6*
*Since joining Seattle

Clearly, Kikuchi and his rotation-mates are all working on less rest. Has the change affected anyone in a positive or negative manner?

Hard to tell.

Marco Gonzales has rallied in a big way since a forgettable first-half. Chris Flexen has continued to remain his consistent self. Meanwhile, Logan Gilbert and Kikuchi have each experienced a rough July and August. Is there any proof of a correlation between the change in rest days and their recent skids?

Nothing definitive.

We know Gonzales prefers the five-man rotation. He’s made that abundantly clear in the past. Yes, Gilbert has been struggling more recently. But he’s a rookie. Therefore, his difficulties may be nothing more than growing pains. And what about Kikuchi?

The effect of shifting to a five-man rotation on Kikuchi is something the Mariners are far more equipped to address than someone writing a blog. Having said that, he’s never delivered consistently good results as a member of a five-man rotation since joining the team.

Seattle used a five-man rotation during Kikuchi’s rough rookie season in 2019. Last year, advanced metrics suggested he was performing better than many believed, but the team used six starters. This season, Kikuchi was at his best during the period the Mariners used a six-man rotation.

Catchers Didn’t Matter

I quickly explored whether Kikuchi performances varied noticeably with different catchers. Since encountering his recent troubles, two players have served as battery-mates – Tom Murphy and rookie Cal Raleigh.

Kikuchi Results Based On Catcher Since July 7th
PA
K%
BB%
AVG
wOBA
xwOBA
Cal Raleigh
134
26.1
8.2
.300
.404
.387
Tom Murphy
74
23.0
12.2
.313
.408
.373

Results-wise, there isn’t a glaring difference between Kikuchi’s stats whether Murphy or Raleigh is catching. Yes, there’s been a higher rate of walks and fewer strikeouts with Murphy behind the plate. Nevertheless, overall production numbers have been bad regardless of backstop.

What Next?

Perhaps Kikuchi begins leaning more heavily on his cutter again. He did just that with 50.8% cutter utilization and 40% ground ball rates in his August 26 start. Maybe the third-year major-leaguer cracks the code on his reduced fastball velocity. If these things were to happen, the Mariners would have a far better shot at reaching the postseason this year.

If Kikuchi doesn’t get back on track, Seattle’s decision regarding the four-year option the club holds on his contract becomes academic. Justifying a long-term commitment would be difficult.

Yusei Kikuchi's MLB Career
ERA
AVG
BB%
SO%
wOBA
xwOBA
2019
5.46
.295
6.9
16.1
.368
..338
2020
5.17
.238
10.3
24.2
.299
.283
2021
4.33
.234
8.9
25.3
.320
.334
MLB*
4.27
.247
7.7
22.8
.316
.318
* Average For Starting Pitchers in 2021

Yes, Kikuchi does have value. But his 2021 stats are average-ish, at best. Teams typically don’t commit four-years and $66 million to a 30-something with these kind of numbers and a history of inconsistency.

Having said all that, Kikuchi still has an opportunity to rebound, deliver All-Star level results, and help his team vie for the postseason. But time is running out for both the player and the Mariners.

If Kikuchi can make a positive and long-lasting impact beginning with his next start, it’s possible the 2021 season can be salvaged for the Mariners, the team’s fans, and ultimately Kikuchi. Otherwise, his days may be numbered in the Emerald City.

That would be unfortunate.

My Oh My…

Got a take on what you just read? Talk about it here!

Image courtesy of Brian Rothmuller/Icon Sportswire
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Luke Arkins

Luke is a native New Yorker, who grew up as a Mets fan. After the US Navy moved him to the Pacific Northwest in 2009, he decided to make Seattle his home. In 2014, Luke joined the Prospect Insider team. During baseball season, he can often be found observing the local team at T-Mobile Park. You can follow Luke on Twitter @luke_arkins

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