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Jalen Beeks is walking a fine line

How much longer will his success continue?

MLB: Tampa Bay Rays at Miami Marlins Steve Mitchell-USA TODAY Sports

It’s fair to worry about Jalen Beeks.

While Beeks began the year playing an interesting swing role in the Rays’ creative bullpen structure, where he was given both important short relief appearences, and occasional multi-inning work, the injury to Tyler Glasnow pushed Beeks closer to a traditional fifth-starter/bulk guy role—at least as close as the 2019 Rays get.

Since then Beeks has pitched every fifth day, chipping in between three innings and five innings each time, except for one excellent appearance against Kansas City where he pitched six and two thirds scoreless. He’s basicaly been a one or two times through the order pitcher, and on the face of it, that’s worked out great for Beeks and the Rays.

For the season, Beeks has produced a 2.73 ERA and a 2.94 FIP, both of which are outstanding. The third stat in the common saber slash line is the one that gives pause though: 4.47 xFIP.

Of the 129 pitchers to have reached 50 innings pitched this year, that’s the largest difference between the two in that direction (a higher xFIP than FIP).*

*Fun fact, the second highest is former-Ray Jake Odorizzi, and the highest in the other direction is former-Ray Drew Smyly.

Simply put, that means that a very large part of Beeks’s run prevention is coming from the fact that he hasn’t given up home runs. He’s only allowed one so far, on 51 fly balls and 38 line drives. That’s a 2% HR/FB figure, and the league average is right now sitting at 15%.

In general, HR/FB is noisy for pitchers, and you can’t look at their results, even in a full season sample size, and be confident that they have a special skill at preventing home runs. And watching Beeks pitch, I can think of no reason to think he in particular should have a special ability at this.

So enjoy the sub-3.00 ERA, but don’t expect it to continue.

MLB: Minnesota Twins at Tampa Bay Rays Kim Klement-USA TODAY Sports

Coming into this 2019 season, Beeks made a few major adjustments:

  • Hiding the ball better throughout his whole delivery.
  • Scrapping his “cutter” and working on a “slider” for his hard breaking pitch (the actual movement on the pitch is very similar, year to year, so this is something I’m kind of taking his word on—he mentioned it to Neil Solondz on the excellent This Week in Rays Baseball podcast)
  • De-emphasizing that hard breaking pitch overall, and instead emphasizing his changeup. Basically, in 2018 Beeks threw the hard breaker against batters of both handedness, and the changeup only against righties. In 2019, that’s flipped, and batters on both sides of the plate get the changeup, while only lefties get the hard breaker.

When a pitcher throws a pitch more often, batters will start looking for it, and his results with that pitch should get worse. Similarly, when a pitcher throws a pitch less often, batters will stop looking for it, and his results with that pitch should get better.

So nothing should be surprising about the fact that the per-pitch results on Beeks’s hard breaking ball have gotten better as he has thrown fewer of them.

It’s a testament to the quality and deception of his change, that with the additional use, its results have stayed good, but I do wonder if the trade-off has gone too far.

Here is whiffs per pitch between the two years.

And here is slugging percentage off each pitch.

Now that Beeks’s hard beaking pitch is infrequently used, and mostly against same-handed hitters, it’s become far and away his most effective offering. Hitters both miss it most often, and hit it weakly when they do manage to put it in play.

Nash Equilibriums vs Discrete Pitch Systems

The simple way to analyze pitch mixes is to think of all pitches as a single system, and to say that, given the optimal mix, the per-pitch results of every pitch should be equal. This model describes a lot of reality, and can be very useful, but it’s also very obviously missing a ton, and this lost complexity is surely part of the explanation for why Beeks’s changeup still works so well this year, despite exposure.

For one, location matters—a slider on the back foot sets up something different than backdoor slider.

And for two, not all pitch interactions are equally strong.

Throwing more sliders against righties isn’t going to change the extent that lefties are sitting on it. And a slider tracking in on the hands against a righty will have a different effect on whether the batter is ready for a fastball at the top of the zone than on whether he’ll be ready for a changeup low and away.

The reality of pitching is really more about finding those equilibriums within pitch systems, and then also finding equilibriums among the pitch systems.

Pointing out a big difference between xFIP and ERA/FIP is the easy part, but what should Beeks and the Rays be doing about it?

The first bit is “get Tyler Glasnow healthy.” Before going on the IL with a forearm strain, Glasnow was legitimately pitching at a Cy Young contender level, and if he can return and pick up where he left off, it will move Beeks back into the role he filled at the start of the season.

Facing fewer batter, fewer times through the order should allow Beeks to give more effort on each pitch and dip less far into his bag of tricks, and should improve his rate performance across the board. But Glasnow’s eventual return doesn’t mean there aren’t adjustments Beeks can make right now.

So how should Beeks use his hard breaking pitch?

Now we’re out of the realm of data that I can figure out how to present, and navigating by my gut.

Whatever he calls his hard breaking ball — cutter or slider — I think he should throw it hard, and think of it as a part of a pitch system primarily with his fastball.

It should live in the zone, not just off the corner to lefties as it does now. It should touch on the back door, and in on the hands. Also on the back foot, threatening the corner for a called strike. Basically, it should be another fastball, and should — with Beeks’s improved delivery deception — help keep hitters off the fastball.

I think the result will be some hard hit balls against his slider, worse per-pitch results, but improved results against his fastball, and a minimal change to the effectiveness of his changeup.

But that’s all theory. I can’t really show any of this. I’m just a guy who writes on the internet. Regression is coming, but true talent can change, and I don’t know how this ends.