Plate discipline has been front and center in the first week of the season. The new automated balls and strikes (ABS) challenge system has allowed batters to eliminate 28 strikeouts and gain 10 walks via challenge, occasionally flipping an out to a runner on base. Defenses’ challenges have generated 13 additional strikeouts and removed 7 walks as well. While defenses have been more accurate overall at this point in the season (58% successful challenges to batters’ 52%), batters have more successfully leveraged their command of the strike zone to determine whether or how plate appearances end. There is, of course, significant variation across batters in how well they’ve performed in their challenges up to this point. Is it due to batters’ differing commands of the strike zone or simply that CB Bucknor has only called 2 games behind the plate? (CB was actually excellent in last night’s Brewers-Rays game according to Umpire Scorecards).
Here at Pitcher List, we have a suite of PLV metrics to study every event in a baseball game at the pitch level. Decision Value is our hitter swing decision metric. It takes inputs like pitch velocity, location, and movement and tells us whether the hitter made a good decision to swing or take a particular pitch. This isn’t quite as simple as plate discipline; swinging at a Logan Webb sinker and pounding it into the ground is a bad outcome even if the pitch was a strike. Instead, Decision Value rewards hitters for swinging at pitches they should be able to hit hard and for taking pitches they’re unlikely to do much with. The flipside is that Decision Value punishes hitters if they don’t swing at pitches they should be doing damage on or do swing at pitches that are unlikely to generate quality contact. You can find a much more thorough introduction to PLV metrics and Decision Value here.
To make our ideas of swing decisions concrete, let’s take a couple of examples of hitters with polarizing 2025 Decision Values. Ronald Acuña Jr. was third in Decision Value last year with a 133 (100 is average, and 15 points is a standard deviation). He did this by chasing less than MLB average (23.2% to 28.4%) but also by being more aggressive in the heart of the zone, swinging at 82.5% of meatball pitches vs an MLB average of 76.3%. When his Decision Value is split out into in-zone vs out-of-zone decisions, he scores highly on both metrics (122 zone value vs 124 out-of-zone value). A player like Elly De La Cruz, who chases at about an average rate but swings at the wrong pitches in the zone, had a 69 zone Decision Value and a 94 out-of-zone Decision Value (82 overall). The bottom of the list includes MLB’s worst players for swing decisions – not that they’re necessarily bad players overall. Javier Báez was last, but Pete Crow-Armstrong and Michael Harris II were both in the bottom ten based on their extreme proclivity to chase.
This leads me to today’s main question: do the batters who understand the strike zone and which pitches are hittable end up faring better on ABS challenges? I’ll approach this via a few case studies since our sample size here is extraordinarily small one week into the season. Specifically, let’s consider the best and worst hitters at using ABS challenges as measured by net runs vs. what would be expected for a player seeing identical pitches, and ask whether this appears related to our preexisting measures for command of the zone.
Our initial table is mostly what you’d expect: batters with excellent command of the zone, plus Elly De La Cruz. Elly was a beneficiary of the aforementioned CB Bucknor horror show in which the Reds had five successful challenges and zero failed challenges. Two players stand out to me, though: Munetaka Murakami and Austin Martin. Murekami is surprising because he’s running an extremely high K rate in his first taste of the majors after regularly running high K rates in Japan. Despite what you might expect, he’s not a free-swinging chase machine – he’s chasing only 26.7% of pitches outside the zone, slightly below the MLB average. Instead, he appears to be an exceptionally passive hitter, swinging at only half of pitches in the zone while MLB swings at more than two-thirds of them. Despite his passivity, he does swing at a higher percentage of meatballs than the rest of MLB and whiffs at a rate that would have led MLB last year, leading me to believe he probably has a pretty good understanding of the zone, but a lot of holes in his swing. Fortunately, you don’t need to be able to hit a ball to be able to tell whether it’s a ball or strike when challenging.
Austin Martin is also interesting. The former top prospect doesn’t swing very hard (68 mph average bat speed), nor does he have much power with his average EVs in the mid-80s and max EVs under 109 mph. Nevertheless, he was 13 percent better than league average at the plate last year on the basis of a strong .374 OBP. He almost never chases, with a career O-Swing of under 19% which is somehow down to 11.4% in the start of the season. Martin’s excellent Decision Value is being driven by his chase rate – his 126 out-of-zone Decision Value was tied for 9th in MLB. He still had a strong 107 zone Decision Value last year, though, underlining his .279 xBA and .403 xSLG. Even if he’s lacking bat speed and his contact rate, while good, is closer to Bo Bichette and Otto Lopez than Steven Kwan or Luis Arraez, he can be an above average bat thanks to his exceptional understanding of what is a strike and what pitches he can handle.
There are some surprising names here, including two of our top three batters in 2025 Decision Value. Leo Rivas led Decision Value last year by never swinging at balls, chasing under 8% of the time (144 out-of-zone Decision Value). His in-zone Decision Value (84) was not great, though, because he also rarely swung at strikes (54.7% of the time, similar to Juan Soto). When he did swing at strikes, he did so at relatively less hittable pitches; he outperformed his xBA and xSLG by 61 and 67 points, respectively. Rivas had an outstanding .387 OBP last year driven by his 18% walk rate. Given how he approaches the zone, pitchers ought to be living in the zone and forcing him to prove that he’s dangerous. So why is he performing so badly on ABS challenges when his offensive game is built around drawing walks? He doesn’t appear to be aggressive enough, challenging only 1 of 5 “reasonable” pitches. He and Dansby Swanson are the only hitters in the bottom 13 by ABS performance that challenge at a below-expected rate. Instead, hitters who perform poorly on ABS challenges, like our 3rd best hitter by Decision Value last year, Ronald Acuña Jr., tend to do so because they’re overconfident in their strike zone abilities. Acuña has challenged three pitches out of 13 deemed “challengeable” by Baseball Savant while their model estimates that an average hitter facing the same pitches would have only challenged one.
At this early stage in the season, it’s tough to draw any firm conclusions about players’ pitch recognition, swing decisions, and challenge performance. Our sample sizes for most metrics are extremely small, and even more so for challenges. As the season continues, though, I’ll be watching who leverages their challenges best and whether that’s another facet of knowing the zone or a separate skill altogether.
