Last week, the Mariners signed a pitcher to an MLB contract. It was not Taijuan Walker, though that still could come. The signing was reliever Yoshihisa Hirano, who will turn 36 in 2020.
Hirano’s 2018 was a success results-wise, and acceptable by peripherals. His 2019 was more of a mess results-wise, though the peripherals were fairly positive. Relievers! Long-time LLer Jake Mailhot wrote Hirano up for FanGraphs, noting the former Diamondbacks’ numbers crashed right before a trip to the injured list, and he looked less sharp upon his return:
After an 11-year career in Japan, Hirano made the jump to the States in 2018. In two seasons with the Diamondbacks, he was a decent option towards the back end of the bullpen. Last year, he improved his strikeout rate by almost four points but saw his FIP jump over four due to an increase in his home run rate. Through August 12, he had actually posted a 3.30 FIP with just three home runs allowed, but a nasty two-game stretch on August 14 and 16 led to a brief stint on the Injured List with elbow inflammation. He returned in mid-September, but continued to struggle, giving up four more home runs in his nine appearances after August 12.
Hirano is a two-pitch reliever, working a near-50/50 split of four-seam fastball and split-finger. As Mailhot notes in the rest of his piece, Hirano ramped up his splitter usage in 2019, from around 45% of the time the year before to 51.4% in 2019. That number could’ve been higher, but after his injury Hirano cut down on splitters, back to 2018 rates.
The splitter is the straw that stirs Hirano’s drink, so to speak. Per Baseball Savant, batters swung at Hirano’s splitters 54.9% of the time last year, compared to just 41.1% of the time for the fastball. That’s despite the fact that the four-seamer was thrown in the strike zone 58.0% of the time while the splitter was in the zone just 25.5% of the time. The pitch looks appropriately devastating, falling off a cliff about two-thirds of the way through its journey.
But like many split-heavy relievers before him, there are two conundrums he’s encountered.
No. 1: How many splitters can be thrown, healthily and safely?
No. 2: How many splitters can be thrown before they lose their deceptiveness?
Neither question has a definitive answer. Splitters have a reputation for being more stressful on the arm, something that seems intuitive even trying to grip the ball and throw it at home. The wide split of the pointer and middle finger around the ball that inspires the pitch’s name tends to tense the forearm, making it a challenging pitch to replicate mechanically. Still, there’s not been definitive research backing up the anecdotal sense of the splitter’s danger, and the recent history of pitchers at the big league level who lean on the splitter is no more injury-wracked than those who don’t. Several pitchers have famously leaned on the pitch for lengthy careers, including Bruce Sutter, Roger Clemens, and John Smoltz, which does not prove its safety but at least shows it is not a surefire career-ender.
For Hirano, perhaps the splitter is a danger, as his elbow injury came after increased use of the pitch last year. But 35 year old pitchers are also wont to be injured, and if Seattle felt comfortable going in on a guaranteed deal, Hirano clearly is starting out 2020 healthy at least. Ultimately, it may not matter if it’s an elevated health risk. For Hirano, entering his third year in MLB and his 14th as a professional, there’s little alternative. He studied and adopted the pitch in 2006, setting the stage for over a decade of success as one of the most dominant relievers in Nippon Professional Baseball with the Orix Buffaloes. If he cannot throw the splitter, his career will have little life left.
The second question, then, leads us to one of my favorite analytical conundrums. Convention and “common sense” say that off-speed pitches derive much of their success from “playing off the fastball”. Fastballs remain the most common pitch in baseball, but their usage has steadily been in decline, with off-speed offerings increasingly becoming primary offerings for pitchers - relievers in particular. Off-speed pitches tend to have better results than heaters, with better whiff rates, worse results on contact, and more swings drawn on pitches outside of the zone.
But is there a breaking point at which off-speed no longer is impactful when a pitcher doesn’t threaten with the “default” fastball? Félix Hernández painfully showed the damage that can be done to an impressive off-speed arsenal when hitters are unthreatened by the fastball, though command played a significant role as well. For many split-finger pitchers, the pitch is only as good as the location, with it almost necessitating placement below the zone to have success. At a certain point, will hitters spit on even the best offerings if they know the chances of the pitch staying in the zone is exceedingly unlikely? The Mariners saw fabulous results with Brandon Brennan in 2019, encouraging him to use his splitter-esque changeup far more frequently, with great results, but Brennan is blessed with a mid-90s fastball that Hirano sits a few ticks behind.
We should expect a similar splitter rate to early 2019 from Hirano for Seattle, perhaps pushing towards 60% or higher. Until hitters refuse to offer at the pitch, there’s no reason not to use his best weapon as often as possible - particularly given his usage will typically be in one-inning stints. Football fans may be familiar with a debate around a similar issue: does a team need to run the ball successfully (or even unsuccessfully) to make play-action passes successful? Convention and “common sense” say yes, the numbers seem to say no, yet logically a breaking point must exist. If he is to improve on his 2019 numbers, we will see Hirano continue to push that edge, until he either rides the wave to the top or crashes down with it.