Is Bobby Dalbec’s Improved Plate Discipline Sustainable?

Given his rise from dark horse to odds-on NL MVP favorite, it’s not a huge surprise that Bryce Harper has been the best hitter in baseball since August 1. Through Sunday’s action, he slashed.346/.464/.795 in 198 plate appearances, good for a 216 wRC+. That performance has catapulted him to the very top of the race, moving ahead of Fernando Tatis Jr. in betting markets as of Monday. A lot thus has been said about Harper, but much less has been written about the second-best hitter over this stretch (among the 251 players to amass at least 100 plate appearances). That hitter, as you could probably guess from this piece’s title, is Red Sox infielder Bobby Dalbec, whose .316/.409/.737 line nearly matches Harper’s, though it has come without the associated fanfare.

That’s understandable given Dalbec’s start to the season. Unlike Harper, who posted very good numbers before his recent stretch of sheer fire, Dalbec nearly found himself without a spot on Boston’s roster following the team’s trade for Kyle Schwarber. Through July 31, Dalbec was slashing just .216/.260/.399, with a 4.4% walk rate, a 37.5% strikeout rate, and 11 homers in 296 trips to the dish. That, coupled with less-than-stellar defense (it’s still rated as a negative), gave the Red Sox every reason to option him to Triple-A. Indeed, as Peter Abraham at The Boston Globe wrote on September 12, “That Schwarber was on the injured list at the time may have been what kept Dalbec on the roster.”

The hot start to Dalbec’s career last season — a 152 wRC+ and eight homers in just 92 plate appearances — seemed unsustainable given the small sample size, 42% strikeout rate, and .394 BABIP. As a result, ZiPS projected him for a 91 wRC+ this season, though Steamer was more bullish at 103. The poor start and the hot stretch since have resulted in season stats — a .245/.306/.497 slashline and 111 wRC+ — roughly in line with what I’d peg as his true talent level.

But what’s interesting to me is the jarring change in Dalbec’s plate discipline since August 1. Strikeout and walk rates don’t need that many plate appearances to stabilize; that he so quickly shifted from being a low-walk, high-strikeout player to a high-walk, low-strikeout player seems truly incredible. The samples are still unequal, but this current stretch seems to be more than just an aberration, at least in the plate discipline department:

To put this in perspective, Dalbec has now walked more times since August 1 than he did from Opening Day through the end of July. That seems to indicate a change under the hood. And yet when we take a look at Dalbec’s plate discipline metrics, there isn’t anything that immediately jumps out as the basis for his much-improved walk and strikeout rates:

You can see some changes if you squint, but none that appear to explain Dalbec’s surge. His contact rates are up, but that wouldn’t explain the increase in his walk rate, or a decrease in strikeout rate of this magnitude. His O-Swing% and his swinging strike rate are both relatively unchanged. Is Dalbec just a case of extreme noise in the discipline department? Maybe, but it’s worth checking the count-specific data to see if an approach change in two-strike counts can explain these results. Maybe Dalbec is generally the same hitter in non-two-strike counts, but has tried harder to avoid the strikeout when faced with one directly. That’s basically what he told Abraham in that September 12 story when he said, “I’m comfortable taking strikes in the zone knowing that’s not the pitch I want. Then just battle with two strikes.”

Indeed, Dalbec’s contact rate on swings with two strikes has jumped by more than 11 percentage points from the first stretch of his season (up to July 31) to the second (August 1 and on). In all other counts, it has actually gone down. Similarly, his swing rate in non-two-strike counts has jumped by about five percentage points, while his swing rate in two-strike counts has dipped slightly. Here’s what all of that looks like in a table:

That all seems good, but of course, there’s still the question of chasing: Is Dalbec swinging at fewer two-strike pitches outside of the strike zone, resulting in these higher contact rates? What’s odd is that his two-strike chase rate hasn’t dipped much between the two stretches: From 39.7% in stretch one to just 36.0% in stretch two. Perhaps when coupled with an increase in his in-zone swing rate in two-strike counts, from 88.2% to 93.2%, we can begin to put together a picture of what is happening. Dalbec is making better swing decisions in two-strike counts, thus yielding more contact and, as a result, fewer strikeouts.

I find this little development intriguing. Dalbec was in the second percentile in two-strike contact rate through July 31. Since, he’s jumped to the 22nd percentile. He’s done it without sacrificing quality of contact, which may not necessarily stick going forward. Baseball is a game of trade-offs, and selling out for contact may reduce one’s power output. (I wrote about this with respect to Dansby Swanson earlier this year.) That dynamic could still come for Dalbec.

Thus, I wonder how sustainable all of this is. While some hitters have a propensity to increase their contact rates with two strikes, the relationship is pretty noisy and may not be a skill that is sustainable year-to-year. In fact, there’s a much stronger association between a hitter’s overall contact rate and their strikeout rate (R-squared of 0.796) than their two-strike contact rate and their strikeout rate (R-squared of 0.258). That’s because a foul ball, while counting as having made contact, doesn’t do much to help a hitter avoid a strikeout since the count does not change. On the other hand, putting the ball in play avoids strikeouts by definition. But given what we know about hitters’ abilities to control their spray angles, being able to specifically avoid fouls and focus solely on putting balls in play might be really hard to for the hitter to control.

Ultimately, my conclusion here appears somewhat unsatisfying. I’m not sure there has been enough of a change in Dalbec’s swing metrics to contend that his recent hot stretch is anything more than noise. Even though he’s had a 25-game stretch with a strikeout rate as low as 20.5%, other strikeout-prone types have done the same. Joey Gallo had a 25-game stretch with a strikeout rate of 24.3% this season; Javier Báez is currently in the midst of a sub-25% strikeout rate stretch; and Tyler O’Neill had one as low as 21.0% in July. Sometimes, even the players who are the most inclined to strike out crush everything and avoid the whiff, but mean reversion eventually runs its course. While it’s been fun to watch Dalbec have so much success, some of his underlying numbers demonstrate that he’s only made slight changes to his swing decisions. As with most players, his full-season stats describe him best, making this stretch likely just a small blip.