Walk-Rate Changes to Buy or Sell

Jeremy Frank dives into early walk rates for 2021 fantasy baseball to find risers and fallers. Some of these hitters may be improving their plate discipline based on BB% while others may not.

About a tenth of the way through the season, it's hard to differentiate between the players who have gotten better or worse from the ones who are simply on a hot or cold streak. As a fantasy owner or a fan, what should the proper reaction be to an April tear? Luckily, some excellent research has been done on how quickly different metrics take to "stabilize" and two that stabilize the fastest for hitters are their strikeout rate and walk rate. For example, it takes over 2.5 times longer to be able to accurately predict a hitter's true batting average based on their season-to-date batting average than it does to accurately predict their walk rate based on the walk rate they had to start the season... and we can use that to our advantage. I'd argue that walk rate matters more for a hitter than strikeout rate in both fantasy and real baseball, so I'll focus this article on the former.

As mentioned, we are only about halfway to the stabilization point for a hitter's walk rate. In 15 games, a guy can get lucky by just facing pitchers who can't hit the zone a few more times than usual. After all, three extra walks in 60 PA is an increase in five percentage points, which is a lot.

Despite needing more of a sample to say for sure who is walking way more and way less, we can look at other metrics to indicate whether a player's early-season outlier may be more or less likely to stick based on them making actual changes versus them getting lucky. There are four categories of players here, and I'll name one or two players that fall under each category.

Legit Increased Walk Rates

Yuli Gurriel, Houston Astros

After posting a walk rate of just 5.8 percent in 2019-20, Gurriel is walking nearly 18 percent of the time so far in 2021. His 13 walks this season are already more than he had in all of 2020. A lot of this could be real, too. While Gurriel is seeing fewer pitches in the zone than usual, he's also laying off them at career-best rates. From 2019-20, Gurriel swung at 36 percent of pitches outside of the zone and 68 percent of pitches in the zone. In 2021? 26 percent and 67 percent, respectively.

The Astros first baseman has managed to swing at about as many strikes while cutting his chase rate by nearly a third. 18 percent is likely higher than Gurriel's true talent level, but even based on 73 PA I'm confident in saying Gurriel's ability to lay off bad pitches is the main reason for his increased walk rate, and by extension his OBP (.452 this season).

Eduardo Escobar, Arizona Diamondbacks

Escobar hasn't had a walk-rate jump nearly to the extent as Gurriel, but I think his is legit too. After walking in 7.1 percent of his plate appearances from 2019 to 2020, Escobar has walked in 12.7 percent of his plate appearances in 2021. With that, Escobar has seen (albeit early) career bests in OBP and SLG despite unpleasant quality of contact numbers.

Traditionally one of the biggest chasers in baseball, the Diamondbacks infielder has cut his from 40 percent to 29 percent while keeping his zone-swing rate relatively constant. He's actually seeing slightly more pitches in the zone than in years past, but has been able to get on base at a much higher clip largely thanks to much-improved plate discipline. Like Gurriel, it's to be seen whether this discipline will hold for the entire season; but unlike other players, his increased walk rate so far has been a product of his improvements.

Increased Walk Rates to Question

Paul DeJong, St. Louis Cardinals 

DeJong's walk rate has risen from just over 9 percent to just over 14 percent, and while that is a very large difference (50 percent more walks!), I wouldn't read too far into it. DeJong is chasing slightly more than usual, which in the scheme of walks is a bad thing. However, the rate at which he has been thrown strikes has decreased by six percentage points. Is this a matter of getting pitched to differently? Or just early season randomness? I'd bet on the latter.

DeJong has actually been thrown breaking/offspeed pitches at a slightly lower clip than in the past, so I don't think it's a case of pitchers figuring something out and trying to pitch around him or getting him to chase. DeJong's historic walk rate is already solid, but I think is a guy that has just gotten a bit lucky with pitchers missing the zone more than usual against him to begin the year.

Legit Decreased Walk Rates

Rhys Hoskins, Philadelphia Phillies

Hoskins has had a very un-Hoskins-like season so far. In recent memory, few hitters have come into the league with discipline like Hoskins, who has drawn walks at a 15 percent clip in his young career. However, in 2021, the Phillies' first baseman has walked just three times in 74 plate appearances. His chase rate is up 9 percentage points, from 25 percent to 34 percent, while only swinging slightly more at pitches inside the zone.

A decrease in walk rate isn't always a bad thing-- say, for example, you're more aggressive on pitches in the zone than usual and cashing in on them. But that isn't Hoskins. Most of his increased swing rate has come on bad pitches and is something that is going to need to change if he wants to get on base more. I trust Hoskins' track record, but at the same time, simply doing what he's been doing and waiting for the early-season small sample to go away isn't going to be enough for him.

Jackie Bradley Jr., Milwaukee Brewers

As much as Hoskins' walk rate has been influenced by his actual discipline, I don't even think it's as drastic as new Brewers outfielder Jackie Bradley Jr. After consistently walking around a tenth of the time in the past, the center fielder has not walked at all in 69 plate appearances and there are many reasons to believe that this is a real problem. His chase rate has increased by 8 percentage points (or 1 out of every 12 pitches more), and his swing rate on pitches in the zone has actually decreased by 6 percent.

This isn't a case of a player swinging at more pitches and by extension walking less due to contact earlier in the count; this is a case of a player who is having much more trouble telling good pitches from bad ones and is walking less because he is swinging at balls and taking strikes. Bradley Jr. has been a regular for the Brewers in center field all season, but there is serious room for concern regarding his plate discipline and by extension practically everything else about his bat, even this early in the season. Christian Yelich's return and Billy McKinney's early-season success may result in a reduction in playing time for JBJ if he can't figure it out at the plate.

Decreased Walk Rates to Question

Jason Heyward, Chicago Cubs

Coming off a career offensive season, Heyward is one of many Cubs hitters who hasn't seen success early on in 2021. Walking 17 percent of the time last season and 13 percent since 2019, Heyward has walked only thrice in 55 PA in 2021 (5 percent). I don't think this is a major concern yet.

Heyward's chase rate is pretty much consistent with the last couple years, and he's swinging at more pitches in the zone which is a good thing when paired with the former even if that means fewer walks. In addition, Heyward has seen one of the largest increases in in-zone pitch rate, by 4 percentage points, while seeing practically the same pitch types he has in years past. Like DeJong but opposite, Heyward's walk rate change is most likely fueled by a small sample and him getting unlucky with pitchers throwing him fewer bad pitches rather than any poor developments at the plate.

Conclusion

It's really early in the season, and a few full count borderline calls could be the difference between a good-looking walk rate and a bad-looking one. However, it is far enough along to look at hitters' underlying statistics, and whether or not their walk rates are fueled more by larger variances brought about by small sample size or instead by actual changes in their tendencies at the plate.

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