The Reinvention of Yusei Kikuchi Is in Progress

One of the most exciting storylines that’s emerged from spring training has been the velocity readings on Yusei Kikuchi’s fastball and slider. It started with whispers during the first bullpens of the year and it was finally confirmed during his first start of the spring. Kikuchi is regularly hitting 95 mph with his fastball and his slider has reached the low 90s. This isn’t a case of a hot stadium radar gun either; these velocity readings have been confirmed by the Trackman system installed in Peoria. All the regular caveats apply when we’re dealing with spring stats, but this increase in velocity is definitely interesting nonetheless.

Kikuchi didn’t exactly have the most pleasant introduction to the major leagues last season. Between the unfortunate death of his father, acclimating to an entirely new country and league, and an overwhelming number of voices speaking into his process, he simply couldn’t find any success on the field. He did make a healthy 32 starts so that has to be taken as a positive, especially since he came over from Japan with a few injury concerns.

The biggest problem for Kikuchi was maintaining consistent mechanics throughout the season. His throwing motion is a little more complex than most. A slight hesitation at the peak of his windup, a long arm motion, and an inconsistent leg kick as he completes his pitch meant that if any one of those components was out of whack, his velocity and command suffered. As he continued to tinker with his mechanics throughout the season, he picked up a number of bad habits that led to him throwing with maximum effort with no gain in velocity. In fact, his average fastball velocity dipped as the season wore on. Through the first two and a half months, his fastball averaged 93.6 mph, but beginning with his start on June 18, he averaged 92.2 mph on his heater through the end of the season.

Kikuchi spent all offseason working on simplifying his mechanics. He spent time at Driveline Baseball to develop a shorter arm path to help him throw with consistent high velocity without sacrificing command. Here’s a decent look at what those revamped mechanics look like, courtesy of Ryan Divish:

The hesitation in the windup is gone and the whole motion is a lot smoother without the hitches that plagued him last year. All that work has translated to higher velocities during spring training. In his first start of the spring, his fastball ranged from 93 to 95 and he’s hit 96 a handful of times in his two starts since then. Even more intriguing are the reports on the velocity of his slider. Shannon Drayer reported that his slider was sitting around 90-91 mph and might have reached 93 in his second start of the spring.

The results have been intriguing but inconsistent. He’s allowed four runs in six and two-thirds innings and has walked five batters. But he’s also struck out ten resulting in an impressive 32.2% strikeout rate. The walks are a little concerning, but are to be expected from someone still getting comfortable with their new mechanics.

Obviously, these spring results have to be taken with a grain of salt. And since we don’t have publically available pitch data for these spring games, it’s hard to perform any meaningful direct analysis on the effectiveness of his increased velocity. Instead, we can come at it from another angle. Last year, Kikuchi threw 1,287 fastballs, with their velocity ranging from 87 mph to 97 mph. If we break up his fastball’s velocity into one mile per hour buckets, we can see how effective the pitch was as it gained or lost speed.

When Kikuchi was able to throw his fastball over 94 mph, it was so much more effective. But as it dipped below 92 mph, batters swung and missed much less often, and when they did make contact, they did a lot more damage. His fastball was already pretty good at inducing whiffs, but when he was able to reach back and hit the mid 90s, batters had a much harder time making contact. That’s definitely an encouraging sign for his new velocity readings this spring.

You can see the effect this added velocity has in this video posted to the Mariners Twitter account.

This was from his spring start on March 5. His first and fourth strikeouts came on fastballs that simply overpowered the opposing batters. His deceiving motion paired with above average velocity for a left-hander could make all the difference for him in 2020.

We can perform the same kind of analysis on his slider too. That pitch averaged 86 mph last year and ranged from 81 mph to 90 mph.

The results are a little less stark for his slider at higher velocities. At 87 mph, it’s a pretty deadly weapon but when it was thrown over 88 mph, some of that effectiveness dropped off. But the pitch was also pretty effective when thrown around 84 mph too. In Japan, Kikuchi was known to change the velocity and shape of the pitch depending on the situation. His slider’s zone rate is a good indicator of this tendency. Slower velocity sliders were more likely to be thrown in the zone and nearly half of them were thrown early in the count. But as he ramped up the velocity on the slider, he located them out of the zone more often, trying to get batters to chase.

Because he threw just two sliders over 90 mph last year, it’s hard to tell what kind of effect increasing the velocity of his slider will have this year. His slider was already thrown with above average velocity, sitting in the 81st percentile for sliders thrown by left-handed pitchers. Bumping the velocity up to the high 80s would give him one of the hardest sliders in the majors. Just six left-handed pitchers threw a slider with an average velocity higher than 88 mph last season.

For his part, Kikuchi seems to be pleased with his progress this spring. These were his comments to Divish after his first spring start:

“My mechanics were solid today. They were exactly how I wanted them, exactly how I practiced this offseason. I was able to just go after hitters instead of worrying about my mechanics on the mound in the game. It’s a relief to see the velocity up and back to where it was so early in the spring. Velocity-wise it was good today. It’s absolutely mechanics. That’s what I worked on this offseason.”

As he continues to get comfortable with his new throwing motion and gains some consistency, his command of his fastball and slider should follow. Then, it’s a matter of maintaining that consistency throughout the regular season. Tinkering when needed, but avoiding over adjusting. It’s a difficult balance to find but he seems committed to putting 2019 behind him and forging ahead in 2020 with a new approach and some new heat.