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Reducing fatigue with a six-man rotation

Back in March, I made the argument that the Cardinals should consider moving to a six-man rotation. With the benefit of hindsight, how would the Cardinals have fared had they implemented this proposal?

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It is hard to make any sweeping conclusions based on four postseason games against an excellent opponent, but one of the narratives that has emerged after the Cardinals' early postseason demise is that several players were fatigued by the end of the season, including key members of the starting rotation. Lance Lynn and Michael Wacha struggled mightily down the stretch, and Carlos Martinez saw his season come to an end in late September when he went down with a shoulder injury.

In hindsight, it is easy to look back and say that the Cardinals may have been better off if they had done something to limit the workload of their starters. However, it is quite difficult for a team to be proactive and implement preventative measures in the middle of the season when starters are pitching well. Carlos Martinez may have been a victim of this short-sighted line of thinking, as the team initially planned to limit his innings but changed course because he looked effective and healthy.

Recently, I listed to an episode of Baseball Prospectus' Effectively Wild Podcast,  which contained an interview with Stan Conte, the former head trainer an VP of medical services for the Dodgers. He talked in-depth about pitcher injuries and fatigue, and he argued that the best way to prevent starting pitcher fatigue was to give starters extra days off throughout the season, as opposed to skipping starts or shutting pitchers down entirely.

One extension of this approach would simply involve going to a six-man rotation. Back in March, I argued that the Cardinals should consider a six-man rotation, mainly due to their pitching depth and the need to limit the innings of multiple starters. While Jaime Garcia's setback made such a proposition unrealistic soon after I wrote that article, I think it is fair to wonder if utilizing a six-man rotation would have left the Cardinals starters in better shape heading into September and the postseason.

A lot has been written in recent months about six-man rotations and whether they ever make sense. One of the biggest arguments against a six-man rotation is that it takes 30-50 innings away from each of a team's top five starters and shifts those innings to a lower-quality sixth starter. While it seems possible that giving starters an extra day of rest could lead to them performing significantly better when they do pitch, there is no evidence that such an effect exists. According to Russell Carleton of Baseball Prospectus, starting pitchers do not appear to pitch any better or worse when they have five days rest as opposed to four.

This means that the only way a six-man a move would make sense is if it has a significant effect in reducing injuries and fatigue of the other five starters in the rotation. Back in June, Rob Arthur of FiveThirtyEight wrote an excellent piece in which he showed a strong link between rest and injury rates for starting pitchers. He found a noticeable drop in injury risk for starting pitchers who pitched with an extra day or two of rest. However, he noted that extra rest did not appear to have any effect in reducing the severity of the injuries that did occur. Even so, this finding is potentially significant and could lead to more teams looking into employing a six-man rotation, depending on their particular situation.

An argument could be made that the 2015 Cardinals were a team that could have benefited from using a six-man rotation. Such a move would have reduced the jump in innings for young starters like Wacha and Martinez, who had never had full seasons starting at the major league level. (An enormous jump in innings was one of the factors that Stan Conte cited in his interview as a major predictor of pitcher injuries.) It is also possible that Lance Lynn could have benefited from receiving extra rest throughout the season, since he, too, appeared to be fighting through fatigue by the end of the season.

Of course, one factor that must be considered in any six-man rotation proposal is the quality of the sixth starter. For the Cardinals, a six-man rotation in 2015 would have meant that Tyler Lyons would be starting several games that would have otherwise been started by John Lackey, Jaime Garcia, Lance Lynn, Michael Wacha, and Carlos Martinez. While this may initially seem like a huge dropoff, we should keep in mind that Tyler Lyons has actually put up solid peripherals in his brief time in the major leagues. In sixty innings this season, Lyons posted a 3.75/4.53/3.46 ERA/FIP/xFIP line with a 23.5 percent strikeout rate and 5.9 percent walk rate. By xFIP, which is better at predicting future performance than ERA and FIP, Lyons was actually better than Lackey, Lynn and Wacha in 2015.

If Lyons had been given more starts, it is quite possible that he would have fit in just fine in the Cardinals rotation and pitched on a comparable level as some of the team's other starters. Yes, he would have taken innings away from superior pitchers like Carlos Martinez and Jaime Garcia as well, but it is hard to say that he would have been significantly worse than all of the other Cardinals starters.

Going into 2016, there may be reasons for the Cardinals to consider a six-man rotation once again, but such a proposal could be complicated by the return of Adam Wainwright. When healthy, Wainwright is without a doubt the best starting pitcher on the Cardinals, and the team may be uncomfortable with the idea of taking innings away from him and giving them to someone like Tyler Lyons. Still, Wainwright is already 34 years old and will probably not be pitching at an ace level for much longer. If he declines some in 2016, the gap between him and the other Cardinals starters may disappear, which would reduce the value lost from shifting his innings to another starting pitcher in a potential six-man rotation.

Ultimately, I do not think that a six-man rotation makes quite as much sense in 2016 as it would have this year. Still, we have seen the idea being discussed and implemented (at least for short periods of time) more often than usual in recent years. Given the rate of starting pitcher injuries throughout baseball, it seems likely that the idea of a six-man rotation will not be going away any time soon.