One of my pet theories for over a decade now is that once the Giants get to the dog days of August, they should go to keeping the rotation on a five day rest rotation, even when there is no rest day during a week, usually happens at least twice in August, and sometimes more, because rain outs are sometimes scheduled in August to make up that game. Now there is a study that validates that theory and suggests keeping to it all season long.
ogc thoughts
Josh Parasar published on his website, Paraball Notes, his study of pitching starts, classifying most of them as 4-day, 5-day, and 6-day rest starts. Here is his methodology:
Throughout the 2023 season, there were a total of 4860 starts. Among these, 3877 starts involved the starting pitcher taking the mound with four, five, or six days of rest. I collected data on these starts and computed the Fielding Independent Pitching (FIP) for each one. Additionally, I adjusted the FIP for each start by factoring in the opposing team's offensive capabilities, based on their 2023 weighted On-Base Average (wOBA).
Every 10-point deviation in wOBA that the opponent generated above or below the league's average wOBA of 0.316, resulted in a corresponding 0.32767 decrease or increase in FIP, thereby establishing the "Modified FIP." I compared each starting pitcher's Modified FIP in a particular game against his season-average FIP, thereby generating the final "Modified FIP premium." I then grouped league-wide Modified FIP premiums based on the number of rest days before a start.
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Judging by the Modified FIP premiums, we can clearly see that pitching on five days rest is optimal. In fact, teams across the league benefitted from their 1886 starts on a five-day rotation, collectively saving 102 runs and increasing their combined win count by 10 compared to utilizing four days of rest exclusively. Conversely, the 406 starts made on a six-day rest cycle resulted in a cost of 12 runs and a reduction of 1 win in total compared to the four-day rest scenario*.
The intuition as to why five days of rest is better than four days of rest is that the starters are able to gain a small amount of freshness and stamina without losing connection with their release point and the strike zone. However, having six days of rest makes the starters even more fresh, but comes with the cost of disrupting their pitching rhythm.
That’s basically the rotation I’ve been suggesting the Giants employ during August, when there are weeks where there is no rest day: SP goes every five days, and if there is a game instead of a rest day, either go with an opener or bring in a SP from bullpen or AAA to be the 6th starter. And as Josh recommends in his blog post, ideally this 6th starter is coming in on 5 days rest.
It’s not a huge difference: for a 162 game season, that’s roughly 8.6% of 1886 starts in the study, which saves 8.8 runs, or roughly one win per season. Still, there have been many seasons where one win can make the difference for getting into the playoffs. And this should help the health of the starters. Josh noted when I asked if the conclusions I came to was accurate:
Pros: +1 win per season on average, top starters are more rested for the playoffs, and better overall rotation health can be expected.
Cons: Requires 1-2 bullpen pitchers with close to starter-like stamina and pitch mix (at least three pitches) or strong AAA starting pitching depth, and a bonafide ace would get a couple fewer starts over the course of the season.
On that last point, that really depends on the number of weeks that has zero days of rest in it. The ace won’t be rotated out until there is five weeks with no day off in it. Also, the rotation is usually restarted from the top of the rotation at the all star break, which usually gives the ace another extra start, which would help mitigate any losses through this strategy of rotation management. The ace might still get their normal number of starts, while the back of the rotation will be the ones to lose a start.
Giants Implications
The Giants were basically already doing that with Logan Webb, going every five days. Of course, for this to work, they need to have five good starting pitchers. At the moment, it’s likely Webb, Cobb, Harrison, Beck, and one of Winn, Stripling, DeSclafani, and perhaps someone in the farm system. So this strategy probably won’t work if the back end starters are not that reliable, which is a key component of this strategy, I would think.
Zaidi said in multiple interviews that he’s not looking for more depth starting pitchers, only ace level, and the only ones that could be considered that are Snell, Montgomery, and perhaps Imanaga, hard to say if he’s ace level or not since he’s never pitched in the majors. So there is the possibility that there might be a pitcher or two added to the rotation. With Cobb out for the beginning of the season, that opens up a spot for someone to step up and force the issue.
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