Notable Starting Pitcher Improvements in K%, BB% and GB% for Fantasy Baseball

We constantly try to find the right statistics to examine when evaluating pitchers' performances. And while there are many rabbit holes you can head down with spin rates, Stuff +, and any number of ERA indicators, it all usually comes back to strikeouts, walks, and the quality of contact that hitters are making off a pitcher.

Even though ground balls end up as base hits more often than fly balls, I'm a big fan of ground ball pitchers and I wanted to include ground ball rate in the research I conducted for this article because I will tell you what ground balls never rarely end up being - extra-base hits. And they never end up becoming home runs. Groundball pitchers usually can survive higher contact rates if they can keep the ball in the park and avoid the big inning.

So while strikeouts are sexy and super important for fantasy baseball, I wanted to see if low walk rates or high ground ball rates were as equally important and as strongly correlated with lower ERAs. What I found out was interesting and I hope you read on as I go on a journey in search of some answers about which of these statistics might be the most predictive of ERA.

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How Do K%, BB%, and GB% Affect ERA?

I set out to measure the increase or decrease in strikeout, walk, and ground ball rates for all starting pitchers who logged 80+ innings in both 2022 and 203, A total of 99 pitchers qualified for the sample under those parameters. After finding the change in each pitcher's rates, I then calculated the correlational coefficient between each stat category with the change in each pitcher's ERA from 2022 to 2023.

There are a lot of factors that could be in play as to why a pitcher's ERA changes from season to season and we all know that ERA is perhaps not the best indicator of a pitcher's overall effectiveness. But it is one of the five pitching stat categories that we use in standard 5x5 leagues, so why not use it here if the results that we are ultimately seeking are lower ERAs and WHIPs?

Here are my findings.

An increase in strikeout rate had the strongest relationship with a decrease in ERA. The two are negatively correlated, meaning as one goes up, the other goes down. This makes sense, right? And even though it was the strongest relationship, it checks in with just a -0.44 coefficient. Suppose you need a refresher on correlational coefficients. In that case, they can range from 1.0 to -1.0, and the closer the number gets to either end of the range, the stronger the positive or negative relationship.

A decrease in walk rate had the next strongest relationship with a decrease in ERA. Pitchers who lowered their walk rate were more likely than not to also have lowered their ERA. This is a positive correlation since as one number goes up (or down) so does the other. The coefficient for this correlation was 0.33, so not quite as strong as the relationship between K% and ERA.

An increase in ground ball rate had only a mild relationship with a decrease in ERA. This is a negative correlation of only 0.15 and the weakest of the bunch. It turns out there are a lot of ground ball pitchers who are mediocre or even bad at run prevention, while there aren't all that many high strikeout pitchers who also carry high ERAs (Lance Lynn is the exception, not the rule).

Biggest BB% Changes

Control is so important for MLB pitchers and unless you have some Spencer Strider-type stuff, you're not likely to get away with a double-digit walk rate.

As far as major improvements in control, let's talk about Kikuchi and Steele as Lorenzen and Houser are pretty boring pitchers for fantasy.

Did you realize Kikuchi was this good last year? I honestly forgot until digging deeper into his 2023 season.

His second go-round in Toronto was far better than his first as he dropped his ERA by 1.3 runs and lowered his WHIP from 1.50 to 1.27. There's nothing really in his underlying stats to suggest that it was fluky either as he had a high BABIP (.325) and a pretty normal strand rate of 77%. His xFIP checked in at 3.73, too. A 19% K/BB% was pretty damn good, too. Perhaps Kikuchi is finally ready to reach his full potential and at an ADP of around 275, I think he's a nice value that you could look to take 15-20 picks earlier.

I didn't measure changes in win totals from 2022 to 2023 but if I did, Justin Steele would be at the top of the list as he went from 4-7 in 2022 to an outstanding 16-5 last year, logging 20 quality starts in 30 outings. What's pretty fascinating about Steele is that his numbers in almost every other stat category besides walks stayed nearly the same. He struck out exactly 24.6% of hitters in both 2022 and 2023. His BABIP and strand rates were nearly identical, as were his GB% and CSW%.

But cutting his walk rate in half from 10% to 5% did wonders for Steele as he was also able to pitch deeper into games as a result, upping his average outing from 5 innings per start in 2022 to nearly 6 innings per start last season.

Eovaldi and Wood are our outliers here as far as guys who walked more hitters but lowered their ERAs. Wood had one of his worst years in 2022 with a 5.10 ERA that was a full run and a half above his career mark so he had plenty of room to improve on that mark.

We all know how Manoah's season ended - in ugly fashion with one of the biggest drop-offs in recent memory from what was a very good year in 2022. And I wrote a bit more about Tyler Anderson's fall from grace here (or maybe just his return to mediocrity after a brief two-year uptick).

Biggest GB% Changes

Hendricks got back to doing what he does best - getting ground balls and inducing soft contact. As a pitcher with only a 16% strikeout rate, his run prevention is tied to his ground ball rate a lot more closely than other pitchers who can generate more whiffs. He finished with a 3.74 ERA over 137 innings and looked much more like the 2018-2020 version of himself.

The NL Cy Young winner Snell had the second-best ground ball rate of his career and the lowest hard contact rate (31%) of his career likely because he cut back on four-seam fastballs and increased the number of breaking balls and changeups he threw. The walk rate was just massive, however, at 13.3% and he was lucky it didn't burn him more often as his 86.7% strand rate was fluky high. Wherever he signs, I'll be interested to see if he can repeat his success from 2023 or if the stars aligned for him last year.

Tarik Skubal is transforming into an ace and has raised his GB% every season since his rookie year. He used to have a home run problem, but he fixed it in a hurry and looks to be primed for a huge season. There's not much to say here, draft him with confidence.

Two pitchers raised their groundball rates and still had higher ERAs in this sample - Logan Gilbert and Logan Webb. I have concluded that if your name is Logan, then you are the exception, not the rule. All kidding aside, there are going to be some outliers in the data and both pitchers still had very solid seasons.

On the other end of the spectrum, we saw the ERAs in the second half of this list explode as their groundball rates dwindled. Valdez saw only a modest bump in ERA despite the largest drop in GB% but consider that his decrease was from 64% (a league-high in 2022) to to 52% in 2023. Anything above 50% and you get to keep your "groundball pitcher" card.

Biggest K% Changes

Remember, the results pointed towards an increase in K% as the most highly correlated statistic with a drop in ERA and all of these examples except Mitch Keller provide some anecdotal evidence to back it up.

No one cranked up the Ks quite like Nick Pivetta, who started the year in the bullpen for Boston but finished the season as their best starter. Pivetta finished with a 31.2% K% on the season over 142 innings with a strong 14.5% SwStr% and 30.8% CSW%. He's a popular breakout candidate this season.

From July 2 to the end of the regular season last year, Nick Pivetta ranked (min. 70 IP):

• 2nd K%
• 6th WHIP
• 18th FIP

• 4th Stuff+
• 11th Location+

Fluke? Or can he sustain that level of production for a full season in 2024? pic.twitter.com/vLX9Cfvdla

— The Commish (@CommishFilmRoom) March 3, 2024

Tyler Wells could be a nice late-round value as he should get a chance to start the season in the rotation for Baltimore. As far as Pablo Lopez and Mitch Keller are concerned, it remains to be seen if they can maintain their big gains in strikeouts since both set career-high marks in 2023.

I wrote earlier this Spring about both Verlander and Javier, who had some of the biggest drops in K-BB%. I'm being cautious with both in drafts.

Checking All The Boxes?

To wrap things up and tie a nice little bow on this project, why don't we take a look at those pitchers who were able to make improvements in all three areas? Here are the six pitchers who raised their strikeout and groundball rates while lowering their walk rates last season.

What a breakout year Kyle Bradish had! Now you know why so many people in the industry were bummed out when learning of his UCL sprain in February. He was (or maybe still is) primed for a big year in Baltimore and might be worthy of a stash with how much progress he made last season.

The best pitch in MLB, per Fangraphs (Stuff+):

Kyle Bradish: Slider (171 Stuff+)

Hitters put up a .210 wOBA (.262 xwOBA) with a 36.4% whiff rate against this pitch. pic.twitter.com/dbGbAxuh6s

— Frank Ammirante (@FAmmiranteTFJ) January 24, 2024

More support for Tarik Skubal here, as if you needed to be sold on him. He's looked fantastic in ST already and could be a top-10 pitcher this year. That's not even being overly optimistic, he has it all working and we just have to see him do it for a full season.

Nick Martinez is not someone who was on my radar at all after pitching mainly in relief last season, but it looks like he will get a chance to start in Cincinnati this season. A 55% ground ball rate could certainly help out in a homer-friendly Great American ballpark and his 13.4% SwStr% from last season suggests he could even improve upon his 23% K% from last year.

Logan Webb was a workhorse last season, logging 216 innings but finishing with just 11 wins. His control was immaculate (3.6% BB%) but his increase in strikeouts was relatively minor and still well below his career-best of 26% in 2021. He's being drafted for his floor rather than his ceiling around an ADP of 45.

Logan Gilbert's numbers were nearly identical (or better) across the board yet his ERA jumped a half run. There's not one stat that stands out that could account for it, other than maybe an increase in HR/FB% (+5%). He's ready for another big year for Seattle, though there might be more buzz around some of his fellow Mariners' hurlers such as Bryce Miller, George Kirby, and Bryan Woo.

And finally, we have Joe Ryan, who did everything better and saw his ERA climb a full run to 4.51. His xFIP was 3.75 and xERA was 4.19, so we know he was unlucky somewhere. Like Gilbert, he had some bad luck on home runs with a 16.7% HR/FB% and he saw a 50-point jump in his BABIP from .253 to .305. He likely overperformed in ERA in 2022 by a half run and underperformed by a half run in 2023. He's probably just a 4.00 ERA pitcher.

Well, I hope we learned something today. Or at least we tried to make sense of some numbers. I will stand by my previous assumptions that high strikeout rates, low walk rates, and high groundball rates are all usually good data points to track with pitchers, even if we don't always see the immediate results in their ERAs and WHIPS. Good luck this season, RotoBallers!

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