Rafael Devers Still Has Another Gear

So far, the Red Sox have been one of this season’s biggest surprises. Since Opening Day, the Sox have already increased their playoff odds by 23.6 percentage points up to 61.5%, the second-largest percentage point increase in baseball (Athletics, +25.7).

To reach the pinnacle of the AL East this quickly, Boston has been successful on both sides of the ball, but it’s the team’s offense that has found itself alone at the top of most major league leaderboards. Through games on Saturday, the Red Sox are slashing .269/.334/.445, with the batting average and slugging percentage each ranking tops among the 30 teams. Their .338 wOBA is seven points above the next-best team, the Dodgers, and their park-adjusted 115 wRC+ is three points above Los Angeles as well.

The entire lineup is hitting, but it’s their core five of J.D. Martinez (195 wRC+), Xander Bogaerts (176 wRC+), Rafael Devers (150 wRC+), Alex Verdugo (135 wRC+), and Christian Vázquez (100 wRC+) that have more or less led the way. And though this could easily be an article about any of those five players’ starts, I want to highlight Devers, whose .281/.371/.544 slash line through games on Saturday actually represents one of the biggest under-performances in baseball relative to his batted ball quality.

Devers is running an elite line, certainly, but he also has the fourth-best expected wOBA in baseball, behind only Harper, Soto, and Ronald Acuña Jr. We have known for a few years now that Devers is a really good player — his 133 wRC+, 5.9 WAR 2019 campaign was the 13th-most valuable season in baseball that year — but to see him in a class with Harper, Soto, and Acuña gives me a whole different perception of his offensive prowess. By most of the rate stats, Devers is on pace for a career year, but by the end of 2021, there’s a pretty good chance his slash line will be even better than it is now. And that’s really exciting if you’re a Red Sox fan.

“Rafael Devers is good, but could be even better” is certainly a fun conclusion, but what’s more interesting is to dive deeper into how he’s changed year-over-year. Last season was a bit of a down year for Devers, slashing .263/.310/.483 with a 109 wRC+, but it was mostly an ice cold start that depressed his overall numbers, with an August 9 ankle injury potentially contributing. It seems silly to look into splits for such a short season, but to illustrate this point, consider that Devers’ second half wRC+ was 60 points higher than his first half figure, in roughly the same number of plate appearances (116 first half vs. 132 second). Nothing fundamentally changed in his walk-strikeout profile, but a .370 BABIP (compared to a .274 BABIP) will certainly help to buoy the overall triple-slash.

This season, though, things are different, even compared to Devers’ torrid 2020 second half. To start, you could point to improved plate discipline, and you’d be right. Through Saturday, Devers had walked in 12.1% of his plate appearances, a rate that, if it holds, would be a 55% improvement over his previous career-best. On the flip side of that coin, his 21.2% strikeout rate wouldn’t be the best mark of his career — in 2019, he struck out just 17% of the time — but a six-point decrease from 2020 is certainly nothing to sniff at, either.

That’s all positive, but, as we know, plate discipline is more than just walks and strikeouts. It’s also about finding your pitches and doing damage when they’re in the right spots. As Ben Clemens noted in his recent article on José Iglesias, hitters are generally better off when not swinging, which intuitively makes sense considering how many negative outcomes can result from a swing. As Ben found, since the advent of pitch tracking in 2008, hitters have cost offenses at least 6,000 runs when swinging.

However, we can break that fact down a bit further. Hitters have to swing at some point; standing and watching each pitch go by might be a viable strategy if you or I were trying to reach base versus a big leaguer, but for Devers and the hundreds of other players currently in the majors, a strikeout rate of 100% wouldn’t be ideal. And, indeed, there are advantageous times to swing, but in the aggregate, the value is only created when the pitch in the heart of the strike zone:

As you can see, the only part of the strike zone where the league-average hitter generates positive value is in the heart. And indeed, Devers has both a) swung more at pitches in the heart of the strike zone, and b) has made better batted ball quality relative to his peers (since xwOBAs are up across the league).

The only two hitters in baseball to increase their heart-of-plate swing rate and their heart-of-plate xwOBA by larger margins than Devers (+7.8 swing, +.138 xwOBA) are Anthony Rizzo (+9.0, +.166) and Ryan McMahon (+8.4, +.149). But Rizzo represents something of an outlier among this group, since he swings at fewer than 70% of pitches in the heart of the plate, compared to Devers and McMahon, who are both among the leaders in heart swing rate, each around 85%. The takeaway here is this: Devers is hunting for his pitch and is successfully doing so, even though his slash line hasn’t quite converged with his underlying metrics just yet.

As any infomercial would say, though, “Wait, there’s more.” Devers is not only among the leaders in swing rate on pitches in the heart of the zone, he is also among the leaders in swing rate on pitches not in the heart of the zone, with his 47% rate ranking as the 12th-highest mark among the 158 players who have seen at least 300 non-heart pitches. Given the above chart, that seems bad; the average hitter loses about two runs of value for every 100 swings on non-heart pitches. For Devers, it’s been worse, as he’s lost about 5.4 runs for every 100 swings so far this season. This seems completely counterintuitive to the point I’ve been making: If I’m arguing that Devers’ plate discipline, even under the hood, has taken a step forward, then why is he swinging so much at pitches where the average hitter is quite likely to make outs?

The answer rests in the fact that Devers is not an average hitter. His plate coverage is ridiculous, which is why I’m arguing that there’s an extra gear here. While Devers’ results on swings at not-great pitches have been bad, his batted ball quality has been excellent. Devers has the fourth-best expected wOBA on pitches that are not over the heart of the plate, and he also has the seventh-largest disparity between his expected and actual wOBAs in these situations. Devers’ .359 xwOBA is 51 points above the league-average xwOBA on pitches not in the heart of the zone, but his .264 wOBA is 22 points below the league-average wOBA here.

Here’s a scatterplot showing hitters’ xwOBA on pitches in the heart vs. their xwOBA on pitches not in the heart:

It’s pretty wild that Acuña has a higher xwOBA on non-heart pitches (.518) than on heart pitches (.492). In fact, he’s the only hitter in baseball with an xwOBA above .400 on non-heart pitches, let alone .500; only four hitters even have an xwOBA above .350 on non-heart pitches, with Devers being one of them. This chart shows how hitters generate their production; for someone like Stanton, with his .639 (!) xwOBA on pitches in the heart vs. his .190 xwOBA on non-heart pitches, he has done the majority of his damage when sitting dead-red. But players like Trout, Harper and Acuña are outliers on both ends of the spectrum, crushing balls everywhere. Devers isn’t quite at that level, but he’s close, and there’s nothing wrong with being a slightly-muted version of a Mike Trout– or Bryce Harper- or Ronald Acuña Jr.-type of player.

This is all to say that Devers, while off to a great start, has found himself among the best in baseball just about everywhere in the underlying metrics. His plate discipline has gotten better year-over-year, but even more important than that, his plate coverage has been absolutely stellar. Even when swinging in parts of the zone where hitters probably shouldn’t be, Devers is making solid contact, and those batted balls should start falling for more hits sooner rather than later. If his expected numbers and actual numbers begin to converge, Devers could be in for one of the best offensive seasons in the sport this year.