Here at Pitcher List, we have a suite of PLV metrics to analyze every pitch in a baseball game. Decision Value (DV) 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 flip side is that Decision Value punishes hitters if they don’t swing at pitches they should be doing damage on or 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.
One of the big storylines in this season’s American League playoff race is the Red Sox’s resurgence. After a dismal start to the season, which included the firing of manager Alex Cora, the Red Sox’s record stood at 32-46 entering a four-game series against the Yankees on June 25th. Beginning with a four-game sweep in that series, the Red Sox are on a 32-9 run that leaves them with a 5-game lead over the Tigers for a wild card spot entering play on August 12th. The streak has led conspiracy theorists on social media to claim that the Red Sox have hacked PitchCom or developed some other nefarious means of identifying pitches. Much of the Red Sox’s improvement is due to better pitching. The team has seen a full run decline in ERA and xERA, and a half of a run to three-quarters of a run improvements in FIP and xFIP.
Setting the pitching improvement aside, though, I thought it would be interesting to spend this week’s edition of PLV DV Weekly exploring in what ways the Red Sox offense has improved over the last 7 weeks of baseball. No statistic, of course, should be considered dispositive of whether a team is cheating or not. We know players’ performance varies from game to game; even with a fixed “true talent level,” the best statistical analysis could ever give you is evidence of performance that is improbable based on past levels. But we also know that true talent levels aren’t fixed. Players tinker with batting stances or add new pitches and make any number of changes we can’t identify by watching. Without making additional assumptions, data will never be able to distinguish between genuine player improvement, a hot streak, and an unfair advantage. Fun with selective endpoints can also yield whatever result you happen to favor – the Padres had the worst offense in baseball by wRC+ entering the All-Star Break and have the best offense in baseball since then, but no one thinks they’ve hacked PitchCom. While we’re not going to p-hack our way to a predetermined conclusion here, I am curious as to whether there have been noticeable changes in what the Red Sox are doing at the plate during this extended period of success.
These are the 14 Red Sox hitters with at least 100 plate appearances through the 24th of June. The first thing to note is that the Red Sox were making pretty poor swing decisions over the first few months of the season. This is the expected outcome for players like Trevor Story and Ceddanne Rafaela, but even Roman Anthony had taken a big step back from the 117 DV he posted in 2025. Former Brewers Andruw Monasterio and Caleb Durbin had strong plate approaches to start the season, but on the whole, the team was below average. If you take a PA-weighted average of the DV’s posted by these hitters through June 24th, you end up with a 92.99. Everyday hitters with a 93 DV last year included Masyn Winn, Brandon Marsh, and Jonathan Aranda – not exactly paragons of a strong plate approach.
There have been 12 Red Sox to make 50 plate appearances since the hot streak began. When you compute the same PA-weighted average DV for the team, the Red Sox clock in at 96.98. That’s a 4-point improvement in the team DV, which isn’t nothing, but it isn’t too much either. This isn’t an apples-to-apples comparison, either. The distribution of plate appearances across hitters has changed as well. Trevor Story, notable for his extremely poor plate approach, hasn’t played at all during the streak. Anthony Seigler, a surprising success, has had an above-average approach during the streak and only 22 plate appearances in the first part of the season. If we restrict our comparison to players who appear on both lists, the team had a 93.76 DV through June 24th and a 95.89 DV from June 25th until today.
If a team knew what pitch was coming, one possible area where it might show up in the data is in their zone swing percentage and chase percentage. Tyler Glasnow was famously tipping his pitches in the 2019 ALDS, and the Astros made him pay by (mostly) sitting fastball. Sitting fastball makes sense if a pitcher is tipping, because fastballs are much more likely to be in the zone than other pitch types. This season, 52.3% of four-seamers have been in the zone, and 58.5% of sinkers have been in the zone. In comparison, only 46.4% of sliders, 43.1% of curves, and 40.3% of changeups have been strikes.
Since the hot streak began, the Red Sox have improved their chase rate by 1.5 percentage points, from 32.2% to 30.7%. In that time period, the Red Sox have chased offspeed and breaking pitches (all pitches classified as curves, sliders, knuckle curves, changeups, and splitters on Fangraphs’ pitch-type splits) at a 32.9% rate, roughly around league average. Before the hot streak, they chased soft stuff 33.4% of the time. Their improvement in chase rate turns out to be relatively smaller on softer stuff than it has been on fastballs.
Alternatively, maybe knowing what pitch is coming would lead them to make contact at a better rate. In the later time period, Red Sox hitters had a 69.7% contact rate against non-fastballs, whereas in the first three months of the season they made contact at a 67.9% rate. There are improvements here, but they’re small. The difference in those contact rates is equivalent to moving from the 47th percentile to the 53rd percentile in contact rate. Maybe the team’s success comes from swinging harder and making better quality of contact when they do connect. Possible, except the team ranks 24th in exit velo and EV90, and 25th in hard-hit rate. None of those are an improvement, either, from the start of the season, when they ranked 20th, 24th, and 19th in the same measures.
So, we can rule out better plate discipline and contact quality against soft stuff as an explanation for the Red Sox’s success. The natural next place to look would be at how they handle fastballs. The Red Sox are having more success against fastballs during the hot streak, improving from 24th in EV90 to 15th, despite having a hard-hit rate that has declined by 3 percentage points. The team’s OPS on fastballs was 25th at the start of the season, but has improved to 12th recently. The team has seen 20-point increases in both OBP and slugging across the two time periods, with the OBP increase predominantly coming from a 1.8 percentage-point bump in walk rate on fastballs. Could that be due to knowing a fastball is coming? I suppose so, if pitchers are trying to throw the fastball outside the zone and bait Red Sox hitters to swing, thinking a breaking ball might break into the zone. That seems like an awful stretch to me, though.
One common thread in the conspiracy theories about the Red Sox’s success has been skepticism about the performance of players who aren’t household names. The aforementioned Monasterio has a 113 OPS despite entering the season as a 29-year-old with 592 career plate appearances at the major league level. Of course, Monasterio also had a 111 OPS in limited time with Milwaukee last season. Is he performing much better this year? Not in any serious sense. He has almost identical swing rates to his time in Milwaukee, although he is swinging the bat about a tick harder than last year. Seigler has had a 96 wRC+ in the majors with Boston after posting a 125 wRC+ in Triple-A. He was much better for the Brewers’ Triple-A affiliate in 2025, though, with a 143 wRC+ courtesy of a .285/.414/.478 line.
So what’s the ultimate story behind the Red Sox’s offensive improvement? It’s a bunch of little things, with no smoking guns about what’s going better. Some of this is due to some changes in the composition of the lineup. The hitters who played in the bad first three months had worse DVs than their replacements, especially Trevor Story. Some of this is due to improvement by the hitters who remain in the lineup, with their approaches improving by about 2 points of DV. Some of this is luck; in the first 3 months of the season, the Red Sox underperformed their wRC by 19 runs, while during their hot streak, they’ve overperformed their wRC by 10 runs. But really, by far the biggest change that is driving the Red Sox’s record is better pitching. The team’s ERA and ERA estimators have all improved by half a run to a run. The Red Sox’s K-BB% has improved by 2.5 percentage points. Clearly, pitching improvements can be explained by hacking PitchCom or identifying opponents’ pitches.
