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Breaking down the 2020 breakout starting pitchers

Using swinging strike rate to assess breakouts.

MLB: NLDS-Los Angeles Dodgers at Washington Nationals Brad Mills-USA TODAY Sports

I used K-BB% to identify breakout candidates in this article:

The concept is to look at a high K-BB% (say 18%) and see if any pitcher met that criteria while posting a higher than expected ERA (say 4.00).

As I had mentioned, K-BB% is extremely correlated to ERA and, especially, WHIP. With wins being harder to predict, targeting pitchers who, in theory, should have a lower ERA and WHIP is what I believe to be the most effective way to target breakouts. You’ll note that given the increased amount of strikeouts and home runs, an elite K-BB% has a much higher chance to be accompanied by a high ERA. Blame the juiced ball if you want, but this is trend over the last few seasons. What this means is that there an avenue to predict improved performance. However, it also means that we have to sift through other factors that may prove otherwise.

  1. The divergence of K-BB% and ERA could have much to do with home runs allowed. The propensity to allow home runs is a trait. That is why we must be careful when assessing players like Matthew Boyd.
  2. Many elite strikeout pitchers can carry a K-BB% that is excellent in their initial decline post-prime. We must be careful to identify a K-BB% that is a result of inconsistent performance or trends in the overall performance.
  3. An extension of point number two is to pay attention to the drivers of K-BB%. A reduction in fastball velocity along with a high K-BB% is something I am skeptical of.

I have already mentioned a strong correlation to ERA and WHIP. Hence, we would expect K-BB% to be strongly correlated to other stats like K%, K/9, FIP, xFIP, SIERA. These are no surprises based on what we know now.

However, K-BB% is also 55% correlated with O-Contact% and 71% correlated to Z-Contact% (70% correlated with Contact%). Stats are based on the entire 2019 statistical population. I will focus on SwStr% - swinging strike percentage. This has a 76% correlation factor with K-BB%, the biggest predictor of K-BB% other than anything that would is calculated similarly to ERA or WHIP (i.e. FIP, xFIP) or has K/BB in its formula (i.e. K/9).

Taking this a step further, there is a correlation of 83% between SwStr% and K%. I want to find out which pitchers are missing bats at a much higher clip than striking batters out. In other words, I want to find pitchers that have a very high ratio of SwStr% to K%. So I did this for every single pitcher in 2019. Note that the results were extremely similar if you use SwStr%/K% or SwStr%/(K-BB%). The average ratio of SwStr% to K% is .49:1 – or 49%.

First, lets look at those notable pitchers with a low SwStr% relative to K%, meaning they are striking out more batters than we’d expect. These notable pitchers are candidates to regress negatively:

  1. Tyler Glasnow – 36%
  2. Jordan Yamamoto – 37%
  3. Adrian Houser – 38%
  4. Chris Bassitt – 39%
  5. Jake Arrieta – 39% (and he was already bad)
  6. Sonny Gray – 39%
  7. Luke Weaver – 40%
  8. Chris Sale – 40%
  9. David Price – 40%
  10. Brandon Woodruff – 40%

Now the fun part. Which pitchers can we expect to see an improved K-BB%? It would give me even more confidence in a pitcher who was already pegged to break out based on K-BB% vs. ERA if they were also pegged to improve K-BB%.

1. Dylan Bundy – 56%. He did not make the breakout list because his K-BB% was only 14.9%, but his swinging strike rate is 12.9%.

2. Griffin Canning – 55%. In the majors last year, he had 13.8% swinging strikes and a K-BB% of 17.3%.

3. Luis Castillo – 55%. If we are talking about absolute ceilings, Castillo probably is probably top 5 this year. A ridiculous 15.9% swinging strike rate accompanies an already high K-BB%. If he can limit the walks a little bit more, he can easily be a top 5 option at SP.

4. Dakota Hudson – 55%. He managed 16 wins with a 6.6% K-BB%. Castillo only won 15 times with a 18.8% K-BB%. Hudson performed well in wins and ERA but lacked in WHIP mainly due to a high BB%. Again, someone that could improve with reduced walks. This is clearly a blanket statement.

5. Joe Musgrove – 55%. A 12.0% swinging strike rate did not lead to as many Ks as one would expect.

6. Yusei Kikuchi – 55%. A 8.8% swinging strike rate is one of the worst in the league. So, he’s bad at getting batters to swing and miss. However, he’s even worse at striking out batters. He can be ignored.

7. Masahiro Tanaka – 55%. His whiff percentage on the splitter, his put away pitch, is significantly down. This coincides with a dip in velocity on that pitch. I do not see positive regression for him.

8. Michael Pineda – 54%. He underperformed his K-BB% and he is, in turn, underperforming his swinging strike rate. His walk rate is minimal, so my only concern is that Pineda has been underperforming his entire career. A once elite prospect, now 30 years old, he has the potential to break out.

9. Blake Snell – 53%. As discussed in the prior article, his swinging strike rate is obscene at 17.7% along with a 33.3% K% and 24.3% K-BB%. Snell is primed for a bounce-back. He’s already broken out.

10. Julio Urias – 53%. A 13.8% swinging strike rate is excellent along with a 17.8% K-BB%. He posted a 2.49 ERA and 1.08 WHIP with a 9.6 K/9. Take the numbers with a grain of salt, as he was used in relief. However, he was an elite prospect not long ago. These ratios over 150 innings would make him a top 25 pitcher, which is a huge draft day bargain.

11. Carlos Carrasco – 53%. A ridiculous 14.9% swinging strike rate did not lead to a lot of success. This is another player that has showed up on both lists as a potential positive regression candidate. However, unlike Snell, there is more risk with respect to age and health.

12. German Marquez – 52%. With a minuscule walk rate, Marquez has a chance to bounce back to SP2 form.

13. Noah Syndergaard – 51%. A 12.5% swinging strike rate is low for Thor, but his K-BB% is also down below his career marks for two consecutive seasons. Like I said, I see some improvement, but nothing indicates he can elevate to elite form.

14. Mike Soroka – 51%. Here is an interesting one. His swinging strike rate was 10.3%. Soroka was excellent and, if he can miss more bats, he can become elite. He was a strikeout pitcher in the minors so it is not out of the question that he can strike out a batter per inning. If he can do this, he can vault from an SP3 to a back-end SP1.

15. Domingo German – 51%. A very respectable 6.6% BB% and 19.2% K-BB% accompanies an excellent 13.0% swinging strike rate. His velocity was down this year but he ended up introducing a slider to his repertoire near the end of the season. This data further solidifies him as a breakout candidate.

Other Notable Breakout Candidates

1. Andrew Heaney – 49%. This solidifies that Heaney is a breakout candidate, as he has underperformed his K-BB% but did not outperform his swinging strike rate.

2. Dinelson Lamet – 41%. A 14% swinging strike rate does not do justice to a 33.6% K%. However, his velocity is up and he’s introduced a sinker. This has resulted in the whiff rate for his slider to be off the charts. When hitters swing at his slider, they miss about half the time.

3. Dustin May – 46%. A swinging strike rate of 8.7% in the majors would not suggest that he had a K-BB% in excess of 18% in the minors and majors in 2019. Digging in a bit more made me realize the value on the post-hype is better than the value on the hype. I’ll likely be targeting Urias over May this season.

4. Matthew Boyd – 47%. This puts him in neutral territory as his K% reflects his swinging strike %.


After looking further into potential breakouts using K-BB% vs. ERA and SwStr% vs. K-BB%, I can give you my personal feelings.

  1. I will be avoiding Chris Sale and Carlos Carrasco based on their current ADPs and risk profiles.
  2. I am confident in a Nola bounce back, extremely confident in a Snell bounce back, and have hope in a Robbie Ray bounce back.
  3. I have changed my tune on Dustin May and am moving into the Julio Urias camp.
  4. SwStr% vs. K-BB% was neutral for Andrew Heaney so I am still completely on board with a breakout.
  5. SwStr% vs. K-BB% showed evidence of potential regression for Lamet, but considering other factors, I’m still all in.
  6. Glasnow and Woodruff I have softened on ever so slightly. I am still targeting Glasnow in drafts but this will make me reluctant to reach on him.
  7. I have no idea what to make of Michael Pineda. What I do know is that his price is right.
  8. I see more room for Domingo German to improve than Matthew Boyd.
  9. Griffin Canning has more upside than I thought.
  10. It is not outside the realm of possibility that Mike Soroka strikes out more than nine batters per nine innings.