Analyzing the Royals’ projected 2021 starting pitchers by CSW rate

So I have been able to contribute recently to Pitcher List, which has been an awesome experience that I didn’t expect when I first started this blog almost a year-and-a-half ago. Not only has it been a great opportunity to write and analyze players and other teams outside the Royals organization (or American League Central), but it has also been a privilege to be able to communicate and learn more about the game from Pitcher List’s incredibly intelligent and well-versed community.

One of the biggest things I have learned about in the last couple of months since following Pitcher List more closely has been Alex Fast’s “Called Strike and Whiff Rate” (or CSW rate for short). Fast wrote a research article on Pitcher List about this metric two years ago, and it has slowly grown to be one of the more used and accepted metrics in regard to analyzing pitchers not just in Pitcher List pieces, but also in other blogging and internet baseball writing circles. The whole article is worth reading, but here’s a snippet from Fast’s piece that explains what CSW rate is and why it’s an effective metric to use when it comes to evaluating and projecting pitchers.

Coined and created by Nick Pollack in the 2018 season, CSW rate stands for Called Strikes + Whiffs and the formula for it is simple:

(Called Strikes + Whiffs)/Total Pitches

It takes into account called strikes, swinging strikes (including blocked ones), swinging pitchouts and foul tips into the glove while excluding foul balls. While the formula may seem rudimentary, the implications are far from it. CSW rate is a simple, fine-tuned and, most importantly, predictive metric that gives us a better glimpse into the true skill of a pitcher.

“CSW Rate: An Intro to an Important New Metric” by Alex Fast; Pitcher List

According to Fast, CSW has a strong correlation to SIERA (Skill-Interactive ERA) rather than traditional ERA. Here is what Fast says about the metric, which should give those unfamiliar with it a better sense of what it is (it can be found on pitchers’ Fangraphs pages typically in the Advanced tab).

[SIERA] is an ERA estimator that suggests strikeouts may be better than FIP suggests, walks are bad but relative to how many you throw, and balls in play are complicated (read here for a deeper dive on SIERA). Most importantly, SIERA is predictive. Like FIP, it can give us a good sense of what a pitcher’s actual skillset is and whether they are over/underperforming their ERA.

“CSW Rate: An Intro to an Important New Metric” by Alex Fast; Pitcher List

I am not going to go into too much depth into Fast’s piece, as it is worth reading alone due to the extensive research from Fast and the PL team. That being said, it has been an interesting metric worth learning about recently, and it has made me curious in terms of how Royals pitchers fared and compared on a CSW basis in 2020.

That being said, according to Fast and his research, CSW “on the whole correlates better to starting pitchers than it does relievers.” This is mostly due to their research finding that it takes around 10 starts to really see substantial CSW correlations to performance, especially when measured by SIERA. However, relievers can be evaluated by CSW, it’s just that it’s not as predictive as starting pitchers, and relievers should only be compared to other relievers when using CSW (though of course, in my first article about a pitcher on Pitcher List, I focused on reliever CSW…sigh).

Thus, in this piece, I wanted to look at the projected Royals starting pitching staff and how they compared in different variations of the CSW metric. The different variations of the metric I used were as follows:

  • 2020 CSW Rate
  • 2020 2-strike CSW Rate
  • 2019 CSW Rate
  • 2019 2-strike CSW Rate

I calculated this metric through a pre-made Statcast search tool on Baseball Savant that I found on the Fantasy Baseball SubReddit. The key thing to pay attention to in the search tool is the pitch result tab, as it was set in all categories that could be counted as either a “called strike” or a swinging strike (which also included foul tips, for example). I know PL writers use different tools to calculate CSW, but I found this tool on Baseball Savant to be accessible and easy to adjust across different scenarios.

So, let’s take a look at what the CSW data tells us about the projected Royals starting pitching staff in 2021.


2020 Royal SP CSW rate

So in this first image, I took a screenshot of the results from the query. The “pitch percentage” essentially translates as CSW. Not surprisingly, Brady Singer seemed to be the best of any “possible” Royals starting pitcher in 2021. I did include Jakob Junis in the query, though I do think it is more likely that he transitions to the bullpen in 2021. Surprisingly, despite Junis’ rough season in 2021, he did perform better than Brad Keller on a CSW basis, as his rate was 1.2 percent higher than the Royals’ ace last season.

Singer, Minor, and Duffy make up the upper half of this list, as they post 33, 31.3, and 28.5 percent CSW rates, respectively. Bubic, Junis, and Keller make up the lower half of this list, as they posted 27.3, 26.6, and 25.4 CSW rates.

I wanted to see how they correlated in regard to SIERA, so I created a custom report on Fangraphs. Here is how those six ranked in regard to SIERA:

  • Minor: 4.16
  • Singer: 4.29
  • Duffy: 4.61
  • Bubic: 4.69
  • Keller: 4.82
  • Junis: 5.03

It’s not a perfect correlation, but as one can see the Royals starting pitchers CSW and SIERA data from 2020 do showcase some similarities. Minor overtakes Singer in SIERA, and Keller is higher than Junis in the same metric. Furthermore, it’s interesting to see how Duffy and Bubic rank the same in both rankings (3rd and 4th). That being said, the CSW rates at the top and bottom are close, so it’s not a surprise that there are slight differences in both metric categories for Royals starting pitchers.

Let’s take a look at how Royals starting pitchers fared last year in regard to two-strike CSW:

2020 Royals SP 2-strike CSW rate

It’s interesting to see how things change a little bit when Royals starting pitchers had two strikes. Though he didn’t pitch with the Royals last year, Minor was the best of the bunch in regard to CSW on two-strike counts. That should be a promising sign for Royals fans who were concerned about his 5.34 ERA a year ago with the Rangers and A’s. Another surprise was seeing Duffy in the number two slot in regard to two-strike CSW. Duffy did post a 9.16 K/9 a year ago, which is the second-best mark of the six Royals starting pitchers. Thus, the Duffman showed he could be successful in punching out batters once he got two strikes on them (the bigger issue though for him is home runs, as his 1.61 HR/9 was the second highest mark behind Junis, who had a 2.70 mark himself).

Singer and Bubic were in the middle, which once again is not too big a surprise considering their strikeout rates from a year ago. Bubic actually posted a higher K/9 than Singer last year (8.82 to 8.53), but Singer out-did Bubic in regard to 2-strike CSW by 0.4 percentage points. Thus, one has to wonder if Singer’s K/9 rate would have maybe risen (or Bubic’s rate regress) had the 2020 season been a bit longer.

Considering Junis and Keller were at the bottom in regard to general CSW, it’s not a surprise that they are also in the bottom in regard to 2-strike CSW as well. Again, Keller continues to be an enigma as the Royals’ projected “ace” in 2021: his slider does show some potential (as I wrote before) , but he always tends to rank on the lower end of other advanced metrics in comparison to other Royals starting pitchers, which is not exactly encouraging.

Thus, I wanted to see Keller, Junis, Minor, and Duffy in a larger sample, and thus, I also decided to look at 2019 CSW and 2-strike CSW data. Of course, this eliminates Singer and Bubic from the query, since they did not pitch in the Majors in 2019 (and such data is harder to acquire from Minor League stats).

2019 Royals SP CSW rate

Minor continues to be the strongest of the bunch, as he posted a CSW rate near 30 percent. While that is lower than his 31.3 percent from 2020, the 2019 sample is much more extensive, as Minor threw nearly 2,400 more pitches than last season. Junis was also a bit of a surprise, as his CSW was actually BETTER in 2019 by 1.6 percent in comparison to 2020. Thus, this difference suggests that Junis could be due for a bounce-back in 2021, even if he does transition to the bullpen.

Duffy and Keller also posted slightly lower CSW rates from their 2020 marks over larger samples, though Keller’s difference in CSW rate (0.3 percent) was not as dramatic as Duffy’s (0.9 percent).

And let’s take a look at the last category…

2019 Royals SP 2-strike CSW rate

Unlike 2020, where there was a lot of change in the rankings in regard to CSW from both queries, both sets this time around are more similar in 2019. The order in the two-strike query is pretty much the same from the general CSW 2019 data set, and the percentage differences between each spot in the rankings are pretty similar as well.


So what can Royals fans take away from this data? Well, over a longer sample, CSW becomes more stable and predicative, which is why Fast prefers this metric over others (such as whiff and swinging strike rate) when it comes to evaluating the value of starting pitchers. It will be interesting to see how Singer and Bubic fare over a full 162 game season, as they both showed promise in both categories of CSW from 2020, but their respective samples didn’t quite give as clear pictures as the Royals starting pitchers’ 2019 data sets.

Furthermore, I think Royals fans ought to feel good about Minor and what he can do in 2021 in Kansas City. His CSW rates from the past two years show that he can still generate strikes with regularity, a key trait for a starting pitcher in today’s game. While velocity dip in 2020 is a concern (he ranked in the 20th percentile a year ago), if it does uptick back to normal as expected (it seemed like the wonky schedule of 2020 had an effect on him), Minor could be a pickup who could really boost this Royals rotation even further in 2021, which is exciting to think about, especially with arms like Daniel Lynch and Jackson Kowar ready to make their Royals debut soon.

That being said, CSW is just one data set and it is not a “silver bullet” by any means when it comes to making “exact” pitcher projections, especially coming off a shortened COVID-affected 2020 season. A variety of different metrics need to be used, both in the traditional and analytical sense, to fully evaluate a player, let alone a starting pitcher. Nonetheless, CSW gives Royals, as well as baseball fans in general, another tool at their disposal, and this could be another key piece to help Royals fans properly evaluate all the aspects of a pitcher as well as their value not just in the short term, but long term possibly as well.

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