Matt Wallner's ironic bat speed conundrum

At the beginning of August, MLB.com’s Mike Petriello examined the importance of swinging hard through the lens of four contact-oriented hitters who changed their MO after the All-Star Break. For Anthony Volpe, Victor Robles, Gavin Lux, and Jeff McNeil, a fast swing revolution spurred drastic midseason turnarounds. 

Statcast released new bat-tracking data in May, unleashing a treasure trove of information that further contextualized the way we think about hitting. For example, at the end of Year 1 of the bat-tracking era, we’ve learned that the difference in production generated by fast swings vs. other swings is vast: 

League Average —

• Fast Swings:  .402 wOBA // 53.1% hard-hit rate // +1.2 run value per 100

• Other Swings .243 wOBA // 31.3% hard-hit rate // -3.6 run value per 100 

Whereas Petriello explored bat-tracking metrics via several former slap hitters, I want to take a different approach. What about hitters already touting elite bat speed? Should they always swing fast? And, of equal importance, what happens when they don’t? 

Minnesota’s Matt Wallner is a bat-tracking darling. Among hitters who took at least 200 swings last season, Wallner ranks sixth in average bat speed (77.3 MPH). His Fast Swing Rate — the percentage of swings that clock in faster than 75 MPH — is also good for sixth-best (73.5%). As we would expect, Wallner does far more damage when he swings harder: 

• Fast Swings:   .489 wOBA // 60.4% hard-hit rate // +3.5 run value per 100 

• Other Swings: .139 wOBA // 23.5% hard-hit rate // -7.0 run value per 100 

Even more so than the average hitter, it behooves Wallner to swing fast. One time, as Wallner told MLB.com, he tried to take something off his swing, aiming to “touch the ball” with less of a vicious hack. The result? A weak ground ball to second base after a bat speed of just 62.3 MPH — the slowest on any ball that Wallner put into play last season. He hasn’t looked back since.  

Why would Wallner even experiment — however briefly — with a slower swing in the first place? The idea plausibly originated from Wallner’s overwhelming tendency to swing and miss. Only five players (PA > 200) whiffed at a higher percentage than Wallner in 2024. A large portion of Wallner’s whiffs actually occurred on pitches in the strike zone: His 31.3% Zone Swing & Miss ranked fourth-highest in MLB, behind only Joey Gallo, Jose Siri, and Will Benson, each of whom struck out in over 38% of their plate appearances. 

And if we look at the pool of hitters who accumulated at least 200 PA in either of the last two seasons, the top-seven single-season Zone Swing & Miss percentages belong to Gallo (2), Siri (2), Wallner (2), and Benson (1). Which is to say, this statistic looks a little sticky. 

But Wallner doesn’t really mind whiffing. 

“Honestly, sometimes, I feel like when I strike out more, those are my best stretches,” Wallner said. “There’s some times when I strike out way too much and I’m terrible, like at the beginning of the year. But when I’m hitting homers, I usually strike out more. I’m looking for pitches, being more aggressive.” 

Though the sample size is small, there is some merit to Wallner’s point: From August on, Wallner’s K% dipped alongside his wOBA, though the former eventually plateaued. 

Intrinsically, it makes sense. Wallner is going to whiff and he’s going to hit for power — that comes with the territory of swinging hard. As Fangraphs’ Ben Clemens explored in May, the correlation coefficient between Average Swing Speed and Whiff/Swing is the largest among any of the new bat-tracking metrics. Perhaps a softer swing would remedy Wallner’s swing-and-miss tendencies. But, as Petriello illuminated, the harder a hitter swings, the more damage they will do off contact. Those facts leave Wallner caught in an odd in-between. 

Here’s where we get a little more nuanced. Wallner’s bat speed isn’t uniform. Like all hitters, Wallner has certain zones in which his bat speed lags. When projecting whether Wallner can become a viable long-term option for the Twins — whether he can out-slug his gaudy whiff rate — it’s important to note that pitchers haven’t quite identified the best way to pitch Wallner. They haven’t truly attacked him where his bat speed is slowest. 

And in that vein, I will argue that — perhaps paradoxically — a faster swing would actually help reduce Wallner’s whiff rate. 

Let’s start with the hole: elevated heat. Wallner mashes in-zone fastballs (.397 wOBA) in an era where in-zone four-seam fastballs (FFs) were thrown 55.4% of the time — a new peak for the Pitch Tracking Era — and hit considerably less, with a .472 SLG good for the second-lowest mark since 2014. As such, simply hitting FFs has become an increasingly rarified skill. But it befits Wallner’s entire profile; while he pulverizes in-zone FFs, he whiffs a lot, too. 

Wallner’s In-Zone Whiff Rate vs. Fastballs: 

• 2022: 17.2%

• 2023: 15.6%

• 2024: 15.5% — third-highest in MLB behind Rafael Devers and Kyle Stowers, PA > 200

Wallner can live with a high whiff rate against pitches that he handles. It becomes a potential problem against pitches that he can’t hit. 

We’ll define high in-zone fastballs as those residing in Stacast’s Gameday Zones 1, 2, and 3. Here’s how Wallner performed against those pitches last season, in comparison to the league: 

• Wallner: .095 wOBA // 52.3% whiff percentage

• League:  .283 wOBA // 23.3% whiff percentage 

Across baseball, in-zone heat has proven effective. The league is whiffing less against high fastballs — in part because hitters have developed new mechanisms to train themselves to catch up to these pitches — but, in general, these pitches continue to excel at inducing soft contact. For Wallner, it’s a double whammy of a black hole. 

To a degree, pitchers changed their game plan against Wallner in September. He saw FFs 42.5% of the time, the second-highest single-month percentage of his career. While he fared well (.349 wOBA), there were some red flags: .267 xWOBA and 11 strikeouts, the most in a single month off one pitch. 

To my surprise, the adjustment didn’t come with a significant change in location. The FFs he received in September were more or less in the same place as they were in July and August. But the selection of FFs were simply better — and more tailored to exploiting Wallner’s weakness: 

Average Induced Vertical Break (IVB) of FFs thrown to Wallner, by month: 

• July —   15.5 in. 

• Aug. — 14.8 in. 

• Sept. — 16.8 in. 

The average FF that Wallner saw in September broke two inches less than the average FF that Wallner saw in August, carrying an illusion of rise — a skill maximized with their placement at the top of the zone. 

But just pointing out that Wallner received a higher quality of fastballs isn’t a satisfying answer, either. Because he hits fastballs. Rather, I think the answer to Wallner’s trouble with high heat can be best quantified with bat-tracking data. 

Looking at the complete collection of Wallner’s swings, we see that his slowest in-zone swings are in Gameday Zones 1, 2, and 3. If we narrow the pool to only focus on Wallner’s fast swings — the swings he has the most success on — we see the same result. Even Wallner’s best swings are weakest at the top of the strike zone. Weakest, of course, is relative. The slowest quadrant still generates an average swing of 78.3 MPH. But, in context, that’s a full mile per hour slower than the slowest average in zones four through nine. 

As a quick aside, this isn’t a problem exclusive to Wallner. Kyle Schwarber, whose bat speed is lowest on the outer half of the plate, also has his highest Whiff% against fastballs in that area. Oneil Cruz, who has trouble making contact at the top of the zone, has a slower bat above the belt, by a rather healthy margin. I would love to have the resources to generate a correlation coefficient for the relationship between a batter’s swing speed and a batter’s whiff rate in specific zones against certain pitches, adding a layer of nuance to the surface-level relationship. Because as I propose with Wallner, specifically against FFs at the top of the zone, a harder swing doesn’t necessarily equate to more whiffs. There is room for more nuance as our relationship with bat-tracking data continues to evolve. 

Wallner’s bat speed is slowest up in the zone. As a result, he has trouble catching up to high FFs, spurring a ludicrous whiff rate. That’s why, in these zones specifically, an even faster swing could curtail Wallner’s whiff rate. Because Wallner is right, his strikeouts aren’t a problem. But, Wallner is also right that he is better when he swings harder. Up in the zone specifically, swinging harder would eliminate a portion of the strikeouts — it’s a way for him to lean into his biggest strength while at least partially addressing his weakness. 

This hasn’t really been an issue for Wallner yet, but I expect it to come into play next season. Pitchers should use bat speed like they would a normal xwOBA heat map, devising their attack plan to go after a hitter in zones in which bat speeds are lowest, and try to avoid areas in which bat speeds are highest. Perhaps bat speed is worth chasing — rather than seeking out poor production — since bat speed may lie at the root of the latter. Certainly, it would suit Wallner to stay a step ahead of this trend. Making a proactive approach to swing faster at the top of the zone would allow him to beat the pitchers at their own adjustment.