Predicting Pitcher K-BB% Breakouts For Fantasy Baseball 2023

You will not read an article from me about fantasy baseball starting pitchers that does not talk a ton about the strikeout-to-walk ratio (K-BB%). It is the most important and most predictive statistic out there for evaluating pitchers.

The way to win a fantasy league is to have a few breakout players on your team. If you can find a top 20 starting pitcher late in the draft or on waivers, you're in business! Easier said than done, of course, but not impossible. We spend a lot of time in the lead-up to the season making predictions about potential breakouts, so that's what I'm here to do today.

I will go about this a bit differently this time. Since K-BB% is so important, it's fair to say that the inevitable SP breakouts in 2023 will show significant improvement in this category. I was curious to look into the pitchers that have significantly increased their K-BB% over one offseason and see if there is anything to be learned here. Do they all improve in the same way? Were there any common underlying metrics that stuck out the year prior to the breakout? Questions like that. So that's what I'll be doing here.

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Biggest Breakouts Since 2016

If we're talking about pitchers that added 10 or more points to their K-BB% from one year to the next, that is the full list. The easiest way to add 10 points to your K-BB%, of course, is to have a very, very bad number the year before. This was the case with Giolito who posted that egregious 4.8% K-BB% in 2018. It wasn't very hard to massively improve on such a low number, but fully to his credit, he brought it the whole way up to 24% - an elite number.

I don't think these are very good cases for us since they're so extreme, so let's focus on more common improvements.

The Consistency of K-BB%

The main reason this stat is so powerful is that it has proven to be quite "sticky" - meaning it stays relatively stable year to year. The correlation between year N and year N+1 for all pitchers here is .77. That signifies a significant predictive power here.

If we look at all pitchers with 15+ starts in both 2021 and 2022 and then compare their K-BB% for both years, we see the average change from 2021 to 2022 was just -1.3%. 58% of pitchers in the sample had a K-BB% in 2022 within three points of their number in 2021. 85% of the pitchers posted a number within 5% of the previous year. Only five pitchers out of 101 saw their number change by more than seven points (Eduardo Rodriguez, James Kaprielian, Erick Fedde, and Trevor Rogers for the worse - and only Jesus Luzardo for the better). Very often, when we see huge changes like this - an injury is the main reason. Either they were injured the year before and improved their mark with health, or vice-versa.

Despite all of this, we still are likely to see a handful of pitchers improve their K-BB% by five or more points this year.

The Examples

Now, let's go one by one back through the last seven full seasons of baseball, highlight each pitcher who saw a significant increase in this category, and try to explain why it happened.

2022 Jesus Luzardo (+9.6%)

You could argue that this was mostly about injuries he suffered in 2021 and a more general lack of experience in the Majors. Luzardo was a top prospect for a long time and just didn't have the command and maybe even the confidence on the hill in his first real run as a starter in 2021. You can see that he improved significantly in both K% and BB% to make the big jump.

Interestingly, his SwStr% didn't change that much (14.1% to 14.5%), which we would almost expect after seeing a seven-point gain in K%. He also had a small pitch mix change, dropping his sinker usage by six points in favor of changeups (+3%), four-seamers (+1%), and sliders (+1%).

I'll answer these five questions for each player to track any consistencies:

K% Improvement? Yes
BB% Improvement? Yes
Team Change? Yes
Pitch Mix Change? Yes
Possibly Health Related? Yes

2022 Aaron Civale (+5.3%)

Civale failed to pitch a full year in either season here, dealing with some one-off injuries (wrist and finger). You can see the main driver was the strikeouts, as that increased by 4.2 points while adding another point increase with the walks. He had always been good at limiting walks, and 2021 was a down year in the K% department for him. He had gone around 22% before that and dropped two points in 2021.

His SwStr% improved moderately (a one-point increase), so that's a little bit of a factor. One thing that does stick out is a pitch mix change. He upped his cutter usage by 10 points (25% to 35%), his curveball usage by 12 points (16% to 28%), and his sinker usage by 12 points (10% to 22%), while pretty much ditching the four-seamer, splitter, and slider. It would seem that the most likely explanation for the K% increase here is the pitch mix change, so we'll make note of that.

K% Improvement? Yes
BB% Improvement? Yes
Team Change? No
Pitch Mix Change? Yes
Possibly Health Related? Yes

2022 Shohei Ohtani (+5.0%)

I don't think we should ever really use Ohtani as a player to be compared to, but he certainly took his pitching game to the next level in 2022. We saw a huge gain in SwStr% (13.9% to 16.2%), and a significant change in the arsenal as he threw a bunch of sliders in place of four-seamers. Maybe it was only a matter of time before Ohtani got well into the thirties with K% given how nasty all of his stuff was. He finally pieced together two healthy years on the mound back-to-back and no doubt that experience helped him figure out the best way to use his elite arsenal.

K% Improvement? Yes
BB% Improvement? Yes
Team Change? No
Pitch Mix Change? Yes
Possibly Health Related? No

2022 Brady Singer (+5.0%)

Singer made strides mostly with the walk, dropping from a below-average BB% to one of the best in the league. He threw more strikes overall in 2022 (+2 points in zone rate, +4 points in first-pitch strike rate). He is our first pitcher here who improved without changing his pitch mix, and very interestingly his SwStr% actually fell by a point.

An SwStr% reduction will most often come with a reduction in K% - so it seems like Singer got pretty lucky here. He was second in the league in called strike rate, which is a pretty noisy statistic in most situations. I would call this improvement mostly luck-based, and I would predict a lower K% in 2023 for him - there's not much we can learn from this example.

K% Improvement? Yes
BB% Improvement? Yes
Team Change? No
Pitch Mix Change? No
Possibly Health Related? No

2019 Lance Lynn

Lynn added almost four points to his SwStr% in 2019 and improved drastically in both K% and BB%. It was his first year with the Rangers, so we have a team change here. There was a pitch mix change as well as he piled on to his four-seamer usage (45% to 54%) and increased his cutter a bit (12% to 16%) at the expense of the sinker (32% to 17%). The sinker is the toughest pitch to get whiffs with, so a drop in sinker usage usually will coincide with an increase in SwStr%.

The reason Lynn has been so good for the last four years or so, we think, is because of how well he tunnels his three fastball variations. He throws a bunch of four-seamers, but they look a lot like the cutter and sinker when coming out of the hand - making it tough for the hitters to know which way it will be moving until it's too late.

Lynn is a pretty unique pitcher, so he's not a great example to learn from - but we can say that this was likely at least partially driven by a pitch mix change.

K% Improvement? Yes
BB% Improvement? Yes
Team Change? Yes
Pitch Mix Change? Yes
Possibly Health Related? No

2019 Sonny Gray

A lot of you probably remember this as the "escape from New York" season for Gray. He showed all kinds of promise early on in his career with the Athletics but then fell apart in New York, only to have a resurgence in 2019 with the Reds.

He didn't see a huge change in SwStr% in 2019, but there was a one-point improvement there going from 10.8% to 11.8%. He is another guy here that benefited from reduced sinker usage (30% to 20%). He traded those sinkers in for sliders (15% to 20%), so we follow that general rule here that trading sinkers for breaking balls can be a driver of what we're looking for.

I'm not sure if I really buy the "pressure of New York City" narrative with Gray - but it's out there and it could have some truth to it.

K% Improvement? Yes
BB% Improvement? No
Team Change? Yes
Pitch Mix Change? Yes
Possibly Health Related? No

2018 and 2019 Gerrit Cole

Few pitchers have improved more in one season than Cole did after escaping Pittsburgh. He actually grew his K-BB% substantially two years in a row. You probably know what happened, the Astros simply unlocked his potential by having him throw more four-seamers (at the expense of, you guessed it - sinkers), throwing them high in the zone, and also by maybe giving him some sticky stuff to use so as to increase his spin rate.

Whatever it was, Cole was another special case. A very talented pitcher just needed to get with the right coaching staff; not super helpful for what we're doing in this study.

K% Improvement? Yes
BB% Improvement? Yes
Team Change? Yes
Pitch Mix Change? Yes
Possibly Health Related? No

2019 Shane Bieber

This was probably caused just by experience. He showed great signs in his short rookie year in 2018 and then took it to the next level in 2019, and he's been a fantasy ace ever since. It wasn't hard to see coming from a rookie with good stuff and great command - so this isn't a great learning case either. That said, he did undergo a pitch mix change as he evened things out after throwing a ton of four-seamers in 2018 (57% usage and he dropped that to 46% in favor of sliders and curveballs).

K% Improvement? Yes
BB% Improvement? No
Team Change? No
Pitch Mix Change? Yes
Possibly Health Related? No

2019 Kevin Gausman

The story here was the splitter. Gausman upped the splitter usage from 24% to 38% and vastly improved the pitch as well (25.3% CSW% to 30.7%).

K% Improvement? Yes
BB% Improvement? No
Team Change? Yes
Pitch Mix Change? Yes
Possibly Health Related? No

2019 Tyler Mahle

Mahle actually lost a half point on his SwStr% in this season, but you can see that he really had a great year with the walk rate. That change didn't stick around after 2019, as he's had a walker rate above 8% in every other season of his career.

He actually completely scrapped his slider in 2019, but then brought it back and has thrown it a good amount each year since. He threw a bunch of curveballs that year and introduced a splitter, so it was a massive pitch mix overhaul that maybe took the league by surprise only for them to adjust to him later on.

K% Improvement? Yes (slight)
BB% Improvement? Yes (huge)
Team Change? No
Pitch Mix Change? Yes
Possibly Health Related? No

2018 Blake Snell

This was Snell's Cy Young award-winning season. People knew he had plenty of upside with his previous prospect pedigree, but he didn't show us much in 2017 with a bad 11.4% SwStr%. Snell improved massively in both K% and BB% that year, and he did undergo a slight pitch mix change as he dropped his four-seamer usage from 55% to 51% in favor of curveballs (+10% usage).

This could be a useful template for us as we just look for some of the pitchers that were expected to do great things when entering the league but then struggle for a year or two to make the jump to that level of competition. We'll keep that in mind when looking at 2023 pitchers.

K% Improvement? Yes
BB% Improvement? Yes
Team Change? No
Pitch Mix Change? Yes
Possibly Health Related? No

2017 Corey Kluber

This example was probably the result of everything just coming together for one year for an already good pitcher. Kluber had been a very good pitcher prior to 2017, and was a good pitcher for a couple of years after 2017 - but this year, he really took everything up a notch.

This year was his peak curveball usage season (28%), and he brought that up from 19% the previous year. We saw him reducing the sinker and four-seamer usage there, so once again - the "breakout" was helped by fewer fastballs being thrown.

2016 Robbie Ray

This one was a little strange, but it turned out to mean something as Ray kept being a pretty good pitcher after this 2016 season. He was a pretty young pitcher at the time, as 2016 was just his second full season in the bigs. He did not change his pitch mix, and you can see that the walk rate actually got worse - it just seems like his pitches got better in 2016, so there wasn't much of a way to predict that back then.

K% Improvement? Yes
BB% Improvement? No
Team Change? No
Pitch Mix Change? No
Possibly Health Related? No

What Did We Learn?

I see two common threads here that would be something we can look for as we turn out focus onto 2023.

1. Health - finding good pitchers that just weren't playing healthy last season.
2. Pitch mix change - specifically ditching fastballs (sinkers mostly).

Guessing at Breakouts

Potential Breakouts Due to Health

#1 Jack Flaherty, St. Louis Cardinals

It's fair to have a ton of doubt about if Flaherty can stay healthy, but health was certainly at least mostly to blame for his 6.6% K-BB% in 2022.

Flaherty had been pretty darn good with his K-BB% prior to last year when everything really fell apart. He made just eight starts and never really got it going with a 19.8% K% and an 11.3% SwStr%. Assuming health, I have no doubt that the K-BB% will jump back up above 17% or so - and that would be a smash at his current ADP of 220.

#2 Eduardo Rodriguez, Detroit Tigers

I'm not sure if this was "injury" as much as just general disinterest in being a professional baseball player - but maybe I'm speaking out of turn. There may be more to this, but the truth is that Rodriguez has not pitched much in the Majors since 2019 for a variety of reasons that don't make a ton of sense. That makes it even tougher to believe we'll get 20+ starts from him in 2023, but it's certainly possible, and his ADP is well after pick 300, so there's very little risk to making this pick.

Rodriguez's strikeout rates since 2015: 18.8%, 22.1%, 25.8%, 26.4%, 25.0%, 27.4%, 18.4%

If he reports to Spring Training on time and seems healthy and looks like his normal self in the first few outings, I would be very interested in drafting Rodriguez as a late-round starter.

#3 Freddy Peralta, Milwaukee Brewers

The 2021 season might turn out to be Peralta's career year as he posted a sweet 24.2% K-BB%, but that fell to 18.6% in 2022 as he made just 17 starts due to a lat injury. There is plenty of reason to doubt Peralta has 30 starts in him in 2023, but if he's on the bump - he'll probably pitch very well and I bet he'll get over a 20% K-BB% again. He's a good bounce-back candidate in drafts with an ADP above 135.

Breakouts Due to Reduced Sinker Usage

What I did here was get a list of all pitchers who led their arsenal with a sinker, and then I sorted that list by overall SwStr%. Here are some standouts:

#1 Jordan Montgomery, St. Louis Cardinals

Montgomery is a guy I've already been predicting for a K% increase given his excelled SwStr%. He went for a 14.7% SwStr% in 2021 and then a 13.9% mark in 2022, but failed to turn in a 25% K% season either time. That's not something super likely to be repeated - Montgomery had the third-lowest K% in the league last year among pitchers with at least a 13.5% SwStr%.

He threw his sinker 34.5% of the time last year and put up just an 8.7% SwStr% with it. His secondary stuff got a bunch of whiffs (curveball at 18% SwStr%, a changeup at 24%, and both were thrown 22% of the time), so any change in favor of those two pitches could result in a significant increase in strikeouts. Given that J-Mont has no trouble with the walk (7.7% in 2021, 5.0% in 2022), a few more strikeouts could really be a huge difference-maker for him in 2023.

#2 JT Brubaker, Pittsburgh Pirates

I was saying the same thing about Brubaker a year ago, and no changes were made - but we're here again and he has another chance to tweak his stuff this offseason. Brubaker threw his sinker 41.9% of the time and put up just a 6.3% SwStr% with it. His next most used pitch was the slider at 31%, and it was awesome with a 22.6% SwStr%. Among starters that threw at least 500 sliders, only seven starters beat that number.

Certainly, pitching isn't as simple as "throw your best pitch a bunch," but I can't see why Brubaker would come into 2023 with 40%+ sinker usage again. He doesn't have a good four-seamer (5% SwStr%, 17% CSW%), so that hurts - but evening out the sinker and slider to a 30/30 split would seem reasonable, and that could really elevate his game as he it would almost certainly result in more strikeouts.

#3 Aaron Ashby, Milwaukee Brewers

He is on plenty of people's breakout radar as he had some sick outings last year when he was going right. He put up a 57% GB% and a 26.5% K%, the only pitcher in the league to go over 55% and 25%, respectively. His issue was health and the walk (9.9% BB%), and those are real concerns.

It seems a little bit less likely that a guy like this would reduce sinker usage since that's the easier pitch to throw for a strike. If he is focusing on walking fewer batters, the answer there is probably not to throw fewer sinkers - and that pitch is also the main reason he got so many ground balls, which the Brewers have to like. Anyways, a few more sliders and some improvement around the edges for Ashby could have him turning in a great season for the Brewers, and I wouldn't be surprised to see more massive fantasy scores out of him next year.

#4 Bailey Falter, Philadelphia Phillies

The young Phillies righty is penciled in as the team's #5 starter right now, so job security isn't exactly there. Falter went for a 24.5% K% in a bullpen role in 2021, and that fell to 21.2% in 2022 as he made more starts than relief appearances. He started throwing more sinkers last year, probably because he was trying to eat more innings as a starter, and he increased his sinker usage from 5% to 33% and took 30 points off the four-seamer usage.

When he did throw his four-seamer last year, he posted an above-average SwStr% with it at 10.9%. He also has a slider that posted a solid SwStr% at 18.2%, and he features a curveball as well (12.8% SwStr%). Fewer sinkers and more four-seamers seem like a good thing to try for Falter, especially since he has no trouble throwing strikes (a 4.3% BB% in 2021, 4.9% in 2022). Falter is also basically free in drafts, going after pick 450. One more SP signing would push him out of the rotation, which contributes to that low ADP - but he's a good flier pick even at this point in the offseason.

#5 Logan Webb, San Francisco Giants

Webb led his pitch mix with the sinker last year at 33%, and he got a whiff on it just 5.4% of the time. His other pitches are much better at generating whiffs with a slider at 13.4%, a changeup at 15.4%, and a four-seamer at 13.4%.

This was his second straight season leading the mix with a sinker, and he's had good seasons both times, which makes it tougher to believe he'll want to change anything - but who knows! It would seem that fewer sinkers in favor of any of his other pitches would up the strikeout rate, which fell dramatically in 2022 (26.5% to 20.7%). I have little doubt that Webb's K-BB% in 2023 will beat his 14.5% mark in 2022, and it could do so dramatically with a shift in the pitch mix. I won't be shocked if Webb is a top 10 SP pick in a year's time.

Bonus Picks

Some pitchers that already have the K% side of the equation down and could benefit largely from just improving on the walk rate:

• David Peterson (27.8% K%, 10.4% BB%)
• Hunter Greene (30.9% K%, 9.0% BB%)
• Cristian Javier (33.2% K%, 8.9% BB%)
• Nick Lodolo (29.7% K%, 8.8% BB%)
• Ryan Pepiot (26.3% K%, 16.9% BB%)

Some pitchers with high SwStr% but lower K%:

• Bailey Ober (14.6% SwStr%, 22.5% K%, 4.8% BB%)
• Drew Rasmussen (13.4% SwStr%, 21.4% K%, 5.3% BB%)
• Nathan Eovaldi (13.2% SwStr%, 22.4% K%, 4.3% BB%)
• Roansy Contreras (13.2% SwStr%, 21.1% K%, 9.3% BB%)
• Ken Waldichuk (13.0% SwStr%, 22.6% K%, 6.8% BB%)
• Daniel Lynch (12.7% SwStr%, 20.0% K%, 8.4% BB%)
• Trevor Rogers (12.6% SwStr%, 22.5% K%, 9.4% BB%)

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