Updating Probable Workload for Starting Pitchers Blanco, Brown, and Arrighetti and Evaluating Regression Risk
My June 17 article detailed work load issues for three starting pitchers (Hunter Brown, Spencer Arrighetti, and Ronel Blanco). The gist of the article was that the Astros’ limited starting pitching depth would make it difficult to moderate the work load of pitchers who are likely to exceed their previous high season work load.
I discussed several options at that time for relieving the pitchers’ work load in the future. One option was the return of Lance McCullers Jr. and Luis Garcia from the IL. However, subsequent events dispelled that option. Another option was trading for a starting pitcher. The Astros subsequently did take that essential step, trading for Yusei Kikuchi. And in fact, the recent return of Justin Verlander from the IL and the acquisition of Kikuchi enabled the Astros to utilize a 6 man rotation, which provided some relief for the work load issue.
In the early summer article, I projected future innings pitched for Brown, Arrighetti, and Blanco, arriving at the conclusion that Arrighetti and Blanco faced a higher liklihood of exceeding their previous season high by more than 30 innings, which is a common benchmark. Since the article estimated future innings pitched by simply trending the previous innings pitched to that point in the season, the evaluation was a very rough approximation. Therefore, updating that analysis with one month remaining is a useful exercise.
The Astros are aware of the need to moderate these three pitcher’ innings and may undertake additional actions to do so. News reports indicate that the Astros will soon return to a five man rotation for awhile, and place Blanco in the bullpen. Given that my previous article suggested that Blanco’s work load was the most significant concern, this presumably will help limit his future innings pitched.
For purposes of the current analysis, I will assume: (1) Blanco pitches 15 more innings out of the bullpen and/or in a start; (2) The Astros continue with a 5 man rotation; and (3) Both Brown and Arrighetti pitch 24 more innings (4 starts each at 6 innings). If the Astros take other actions to limit the usage of Brown and Arrighetti (such as returning to a six man rotation) this would alter the number of innings assumed. The table below shows my current estimate for exceeding the previous high innings pitched. (Note the previous high season is based on both minor and major league innings.)
Some observations:
- Previously I projected that Brown would equal his prior high work load in 2023, but now it seems likely that he will exceed his prior high innings pitched by 6.4%. My previous projection of 142 innings for Arrighetti is slightly lower than the current estimate. Given that all of Arrighetti’s previous season high was in the minor leagues and not the majors, the estimated 19.4% increase bears watching.
- Even with a probable return to the bullpen, Blanco is likely to blow through the 30 inning increase threshold by 8 innings. Given that this is Blanco’s first season as a regular starter, the 30.4% increase in his previous season high probably is the most significant observation.
- Neither Brown or Arrighetti appear likely to exceed the 30 inning increase threshold. This threshold is an arbitrary benchmark developed by Tom Verducci. While it is a common benchmark, the 30 innings increase is simply a rule of thumb and has not been proven to be an accurate predictor of injury or performance.
- Verducci hypothesized that this 30 innings increase test, when applied to young pitchers, would identify pitchers who are more vulnerable to future injury or may suffer decreased performance due to overuse. For example, in this 2018 article, Verducci identified Lance McCullers Jr., Luis Severeno, Noah Syndergaard, and Carlos Martinez, as young pitchers who might face future injury risk due to their innings increase. Each of those pitchers subsequently has experienced significant shoulder or arm injures, but there is no proof of cause and effect. In fact, pitching injuries are so common that cause and effect always will be difficult to prove. But it is probably prudent to monitor innings increases encountered by young or inexperienced pitchers.
- The Verducci article doesn’t really cause great concern for the three Astros’ pitchers evaluated here. All of the pitchers listed in his 2018 article experienced an increase in innings pitched significantly higher than I estimate for Brown, Arrighetti, or Blanco. But note that I haven’t considered any potential playoff innings pitched in my comparison. That could raise an additional work load issue if the Astros were to proceed deeply into the playoffs.
Starting Pitcher Regression
Limiting work load is sometimes viewed as a means of reducing pitchers’ fatigue or minor injuries, which can lead to a decline in performance. However, again, there is not a firm foundation of scientific proof for this concept. Indeed, it is difficult to separate decline due to work load from ordinary statistical regression. Increasing the innings pitched may also increase the liklihood of regression to the mean. If a pitcher has experienced some degree of luck which is reflected in his ERA, the simple addition of more innings will provide more opportunity for regression to reveal itself.
Regardless of work load considerations, Astros’ fans should be aware of potential regression risk. The Astros starting pitching has been extraordinary this second half of the season, and any potential regression could affect wins and losses during both the remaining month of the season, as well as the playoffs (assuming the Astros succeed during the regular season).
One way of evaluating regression risk is to compare ERA with Fielding Independent Pitching (FIP) and Expected FIP (x-FIP). Essentially this approach is comparing underlying peripheral pitching stats to the actual earned runs allowed. If the FIP and x-FIP exceed the pitcher’s ERA, this increases the risk of regression (at least in theory). Because the Astros have been riding the crest of exceptional second half starting pitching, my comparison focuses on FIP and ERA performance during the period June 30 to Current. FIP and x-FIP are considered to be more predictive of future performance than ERA.
This comparison averages FIP and x-FIP for period after June 30 in order to evaluate the potential for regression in the pitcher’s second half ERA.
- All of the starters have pitched to a second half ERA below their concurrent FIP and x-FIP. Team fielding may be a contributing factor in this comparison; moreover, it is possible that some of the pitchers’ runs allowed results have been aided by the defense. In addition, several Astros’ pitchers (such as Framber Valdez) have shown the ability to sustain ERAs below FIP. However, it is likely that there may be some future movement of the rotation’s second half ERA in the direction of the FIP.
- Hunter Brown shows the greatest potential for regression, given his low second half runs allowed. His FIP/x-FIP is a relatively fine 3.27, but it is 28% higher than his ERA. This partly may reflect Brown’s increased reliance on “pitch to contact” in order to pitch more deeply into games. But that approach carries the risk of BABIP regression.
- Kikuchi shows the least potential for regression because of his excellent FIP and x-FIP during his Astros’ tenure.
- Arrighetti, Valdez, and Blanco appear to be at medium level risk of regression. Arrighetti and Blanco are more concerning than Valdez, given that their second half peripherals trend in the direction of a high 3-ish or 4-ish ERA. Both pitchers walk too many batters to be entirely comfortable predicting that their future ERA performance will continue at the current monthly rate.
- The regression potential needs to be monitored, particularly as the team assesses playoff roles for the pitchers.
As a concluding point, this analysis shows that the Astros must continue to focus on maintaining good team defense in order to continue the excellent pitching results they have received in August. By avoiding errors and maintaining exceptional range, the rotation can continue to outperform their Fielding Independent Pitching.