What Remains of Clayton Kershaw

For major league pitchers, the end always feels depressingly close at hand. In a game increasingly dominated by power and velocity, losing a tick can be the difference between sneaking a fastball past someone and watching a home run trot. Throw in elbow injuries, blisters, and hitters obsessively watching video looking for any exploitable edge, and it’s a miracle that any pitchers can sustain success.

Clayton Kershaw is no exception to this pattern. He may be the greatest pitcher of the 21st century, but that doesn’t give him special immunity from velocity loss or a license to avoid injury. Gone are the days of Kershaw posting sub-2 ERAs regularly. That’s partially due to the changing offensive environment, to be sure, but it’s also a reflection of the fact that Kershaw is aging. His strikeout rate fell last year to the lowest rate since his rookie season, a pedestrian 23.9%. He made less than 30 starts for a third straight season. His fastball velocity declined 1.5 mph. Age comes for everyone, or so it seems.

When Kershaw returned from a season-opening IL stint, he did so with old-man wiles. His velocity was down another tick, now approaching 90 mph. As Ben Lindbergh ably chronicled, Kershaw’s plan was to stick with what worked in 2018 and survive on sliders and first-pitch strikes. He became perhaps the most extreme pitcher in baseball, piping in first strikes nearly three-quarters of the time and afterward departing the strike zone entirely. He accomplished that trick by throwing his fastball 61% of the time to open at-bats and only 33% of the time after that.

However, even these extreme changes couldn’t hide the fact that Kershaw was slipping. At roughly the midpoint of the season, July 1st, Kershaw was 36th in WAR among pitchers, sandwiched between Kyle Gibson and Sonny Gray. He was marginally better, 24th, by RA9-WAR, but even there, it was weird seeing Kershaw’s name next to Yonny Chirinos and Zach Eflin. Some of this came from a limited workload, but his 3.23 ERA and 3.76 FIP told the same story. It wasn’t just the ball, either: his 77 ERA- and 89 FIP- were his highest since his rookie year, and his 22.7% strikeout rate was down even from last year’s low level.

The magic of the halfway point of the season is that there’s still time to change the narrative. Since the midway point, Kershaw has made six starts. In those outings, he’s been vintage Kershaw — a 1.66 ERA, a 2.43 FIP, and a 32% strikeout rate all look like numbers from Kershaw’s long peak rather than from the last few seasons of being merely above-average. This isn’t a trick of getting a few extra games in pitching-friendly parks in a small sample, either: his 56 FIP- is seventh-best among starters over the interval, and his 39 ERA- is fourth.

Six games is a small sample. Reading too much into a month’s worth of results is a sure way to convince yourself of false narratives. Still, Kershaw’s underlying results back up his improvement — this change looks real, in other words. His strikeout rate didn’t just increase 10% out of nowhere — he started missing bats more, and the strikeouts followed. His slider had generated whiffs on only 28.7% of swings this year as of the beginning of July, in line with last year and far below his dominant peak:

Over his last six starts, it’s back: the slider sports a 40.9% whiff rate. How out of character is that for latter-day Kershaw? In the season-and-a-half between the beginning of 2018 and July 1, 2019, he’d made 40 starts. Out of those 40, only five had slider whiff rates above 40.9%. He’s regained a form, in other words, that he struggled to reach for even a game at a time over the last few years.

Kershaw’s slider isn’t just improving for no reason. He’s throwing the pitch differently, and batters haven’t yet been able to adapt. He’s slowed the pitch down after years of throwing it hard. Out of the 46 starts he’s made since the beginning of 2018, the four with the slowest average slider velocity have occurred since the beginning of July. Kershaw didn’t always throw a hard slider, but he dabbled with it around 2011 and switched to it full-time in 2014, coinciding with his peak. He’d kept that slider velocity even as his fastball lost its zip.

But pitches don’t exist in a vacuum, and the slider’s relationship to the fastball changed markedly. First, the velocity gap between the two pitches crumbled. Take a look at the fastball/slider velocity gap, and you can see a clear pattern. The 2019 data here is again through the beginning of July, excluding his last six starts:

Of course, matched velocity isn’t an insurmountable problem on its own. The bigger problem was that the fastball and slider started behaving more similarly. Kershaw’s fastball has had added glove-side movement over the years, moving closer and closer to the break of his slider. At the same time, its lost velocity gave it more time to fall due to gravity, and Kershaw also got less ride on the ball even after accounting for gravity. In other words, the fastball started moving more like the slider. Take a look at how far apart a fastball and slider thrown at the same starting point end up by year (again, 2019 data is through July 1st):

Wonder why Kershaw’s slider was missing less bats? It simply wasn’t getting the separation, either in velocity or movement, that it needed. Those most recent six starts? They changed the pattern. The velocity gap increased by .9 mph, the movement gap by two full inches. The movement differential isn’t quite back to 2016 levels, but it’s heading that way. Two inches is everything when it comes to missing bats, and giving the slider more time to break and drop was an easy way to get that separation.

Want an evocative demonstration of the value of this added separation? From the beginning of 2018 until July 1, Kershaw got 268 swings at sliders outside of the strike zone. That’s exactly what he wanted — for his career, batters whiff on 63.3% of such pitches. But for 2018 and most of 2019, he simply wasn’t getting those whiffs. Batters came up empty on only 49% of their swings, nearly five standard deviations below his old rate. Pitches that should have ended at-bats resulted in foul balls and gave batters another bite at the apple. For the past six starts, he’s generated whiffs on 69% of the same swings, recapturing his old form.

The extra movement doesn’t only help on out pitches, either. One of Kershaw’s biggest problems early this year was leaving breaking balls over the plate. When batters swung at sliders in the strike zone, it ended badly for Kershaw. He almost never missed bats (15.7% whiff rate), and when batters put the ball in play, they tattooed it to the tune of a .375 wOBA and .410 xwOBA. That wOBA was the highest he’d allowed on zone sliders since 2012.

It’s still a small sample, but batters have been far worse against Kershaw’s slider over the plate over the past six starts. He’s generating misses on 21.6% of swings, solidly better than earlier this year, and the contact hasn’t been as dangerous, either. He’s allowed a .290 wOBA and .332 xwOBA when batters put zone sliders in play. Want further confirmation? Those 29 batted balls have an average exit velocity of 90 mph, down nearly 2 mph from the first half of the year.

Pitching is more complicated than making one single adjustment, of course, and Kershaw has made other changes. He’s leaning even more on the slider when ahead in the count, going to it more than half the time with two strikes. He’s throwing more sliders to lefties and more fastballs to righties, maximizing the platoon tendencies of both pitches. He’s completely abandoned his curveball to lefties until he gets ahead in the count. For the most part though, the new slider is the driver of everything.

Nothing ever lasts. Before long, Kershaw will have lost even more fastball velocity. Time wounds all heels, and no one can outrun it forever. For a month, however, Kershaw has turned back the clock. He’s made a simple adjustment that makes batters’ lives harder, and for now that’s enough. If you didn’t look too closely at the radar gun as Kershaw carved up the Cardinals in his most recent start, you could almost imagine it was 2015 again. Batters flailing over sliders? Curveballs locking knees? A fastball that was miraculously hard to square up? It was all there.

Sometime soon, it won’t all be there. Batters will adjust back. Something else will break, and Kershaw won’t be able to fix it. That hasn’t happened yet though, and dwelling on the future is no fun. Right this instant, Clayton Kershaw is dominating again. Even in a career with such dizzying highs, his 2019 stands out. You can’t cheat time, but you can always try to adapt, and watching Kershaw figure it out on the fly is a delight.