Zack Gelof Is Streaking, but May Need Some Tweaking

The Oakland A’s have not been shy about calling up their top prospects this season, including a slew of the most highly-ranked young players in their system. Many of those prospects have already begun to sculpt the narrative of their early big league careers, to largely disappointing results. Mason Miller dazzled in his first few outings, but was felled by injury soon thereafter. Kyle Muller has bounced between the majors and Triple-A, with a meager mid-teens strikeout rate and an ERA above 7.00 at both levels. Esteury Ruiz has been as spectacular as expected on the basepaths, but his Triple-A offense was a mirage that has dissipated in the majors. And while Ken Waldichuk’s stuff seemed noteworthy in the lead up to the season, his walk rate has ballooned and his fastball was at one point measured by Statcast as the worst in the league, at 16 runs worse than average. As of now, to borrow a phrase, he’s just Ken.

This past month has seen the promotion of three more of Oakland’s promising young prospects: Tyler Soderstrom, Zack Gelof, and Lawrence Butler. The most recent of those promotions was Butler, who joined the A’s major league roster on August 11 after tamping down his strikeouts and finding himself on an ultra-fast track (he started the season at Double-A). With just a handful of games under his belt, it’s too soon to read much into his performance. Soderstrom and Gelof, meanwhile, both debuted in mid-July. And while Soderstrom is the more highly ranked prospect, his bat has been too quiet to make up for his strikeouts at the big league level. Instead, it’s Gelof whose name is currently accompanied by a string of fire emojis in the Baseball Savant search bar.

This isn’t the first time that Gelof has displayed an affinity for outperforming expectations. As he climbed through the A’s minor league system, he never posted a line below league average despite being considerably younger than the players around him. And while offensive numbers coming out of hitter-friendly Triple-A Vegas are never to be fully trusted, he’s continued that pattern with the big league squad, to the tune of a 174 wRC+ thus far as a 23 year old. His speed has factored heavily into his performance, by way of both stolen bases and hustling extra bags out of bloop hits and defensive miscues. But most notable has been his power, which has been nothing short of explosive. Gelof’s hard-hit rate has climbed about 10% as a major leaguer, and 20 of his 37 hits have been for extra bases, including eight bombs, which he has sent out to all parts of the field. The power is particularly exciting, as that element of his game is often cited as his most significant offensive question mark.

The natural next question, of course, is how is he doing this? Has Gelof made an adjustment to his approach? Has his swing changed in a meaningful way as a big leaguer? And perhaps most interesting: If his big league theatrics are a continuation of a long track record of out-performing expectations, is it time for us to update our expectations regarding his future?

As always, context is key, and in Gelof’s case, further investigation into the context surrounding his hot streak throws a bit of a wet blanket over those fire emojis. Despite his on-paper power production, Gelof’s underlying metrics make it more difficult to buy into his thump long-term. His exit velocities are quite low against anything other than four-seam fastballs, and his BABIP is on the high side, as many of his hits have been more of the well-placed than the well-struck variety. Most alarming, though, is his in-zone contact rate, which is in the low 70s, several points lower than any qualified major leaguer this year.

Here is a chart of all of Gelof’s swinging strikes (including foul tips) as a big leaguer, courtesy of Baseball Savant:

While Soderstrom is a very different type of prospect than Gelof, they debuted on the same day and have very similar strikeout rates right now. So let’s take a look at Soderstrom’s swing-and-miss chart as a means of comparison:

The differences between those charts are obvious, and based on that alone, Gelof’s success relative to Soderstrom’s is a bit of a surprise. A mere glance at their respective swinging strikes highlights the troubling in-zone issues plaguing Gelof’s approach, and looking back at his in-zone whiffs as a minor leaguer, it’s hard to pinpoint any improvements or adjustments in that area.

A closer look at where Gelof is making meaningful contact is illuminating. He’s significantly more dangerous up in the zone, with his OPS on in-zone offerings in the upper half sitting at nearly double that on offerings in the lower half.

Here’s a look at all of Gelof’s big league hits this season:

I think his upper-zone proclivity is largely due to the shape of his swing and how it interacts with the shape of the pitches he’s seeing.

Here’s a side view of Gelof’s swing, taken on the backfields last year:

Here, I’ve added a trail to highlight the path of the head of his bat:

The flatness of Gelof’s bat path is easier to notice when compared to a swing geared more toward power. Lucky for us, the video above was taken at a game that also featured Astros outfield prospect Zach Daniels, whose swing has drawn comparisons to Giancarlo Stanton’s due to its predisposition for power. Since he played in the same game, we have video from precisely the same vantage point to compare Gelof’s cut to.

Here’s what Daniels’ swing looked like that night, first on its own, then with a trail:

For good measure, here’s what the two swings look like overlayed and aligned at home plate:

And finally, here’s an overlay of just the shapes created by their respective bat heads. This time, they’re aligned at the point at which they make contact, to get a sense for how each bat interacts with the ball, in particular the steepness of Daniel’s bat path, relative to Gelof’s:

The videos above are from last year, but Gelof’s swing looks the same now as it did then. Indeed, the flatness of his swing has been noted throughout his minor league career. Here’s a look at what his swing has looked like over time, showing how little it has changed:

In the past, I’ve described Gelof’s atypically flat swing as having a softball look to it. But lest that description be misconstrued as a dig against Gelof (or softball), I will assert that his swing’s softbally-ness is exactly what explains the results he’s getting with it.

The differences between softball and baseball are many, but one of the most fundamental, from a mechanics perspective, is the angle from which a pitch approaches the plate. In baseball, the mound and pitchers’ overhand deliveries create a downward angle towards the hitter. In softball, not only is the pitcher throwing from the polar opposite release point (submariners notwithstanding), but the field’s lack of a mound further lowers that release point such that a fastpitch softball delivery creates an upward angle toward the plate. The flat swing typically associated with softball is a direct reaction to this difference in angle, as an uppercut is much more difficult to time against the pitch’s upward trajectory. This is why baseball swings are hard to adapt to fastpitch softball (and why baseball swings are often more effective in slowpitch softball than fastpitch softball swings are, but that’s a discussion for another time).

Now, to be sure, Gelof’s swing isn’t really a softball swing. It’s just that his non-existent load, flat bat path, and the lack of natural lift in his finish combine to mimic the mechanics of a softball swing. It stands to reason, then, that upper-zone four-seam fastballs – i.e. the pitches he sees whose shapes best mimic the typical shape of a softball pitch angle – are the ones off which his swing is playing best (seven of his eight dingers have been on four-seamers at or around the letters). It’s true he hasn’t yet faced many of the sport’s most fearsome ride-inducing flamethrowers, but his first big league home run did come off of Houston’s Ryne Stanek, whose four-seamer has produced some of the least downward movement across baseball this season (his fastball has just seven inches of drop, while the league average is 15 inches):

It also sheds some light on why Gelof struggles to make solid contact against changeups and breaking balls with downward movement. His lack of uppercut requires him to extend his arms in a way that decreases the power they’re producing in order to cover the lower and outer parts of the strike zone:

So, to answer the questions I put forth above: No, Gelof hasn’t demonstrated any obvious adjustments to either his swing decisions, or to his swing itself. Still, his results speak for themselves, though it’s hard not to be skeptical about their long-term playability. As big league pitchers become more familiar with Gelof, it seems inevitable that those flaws will eventually catch up to him. If and when the power dries up, or his weaker contact stops finding unoccupied spots on the field, Gelof may be forced to remedy his in-zone contact issues, particularly in the lower half. But for now, he can afford an ain’t-broke-don’t-fix-it mindset in regards to the strengths and weaknesses of his swing and simply enjoy his status as a rare bright spot for an otherwise bleak 2023 in Oakland.