Relief in Relief Pitching? Starters Can’t Seem To Find It

How much should a team’s postseason strategy differ from its regular-season tactics? Overall, probably not that much; if your club makes it to the postseason, it ain’t broke, so to speak. Further, I generally believe the postseason is not the time to experiment with new gameplans that always carry some heightened risk. But historically, there are myriad ways that teams have shaken things up come October.

This especially seems to be the case when a team is down in a series. Take the Yankees in the ALCS this year — that squad went with three different leadoff hitters in four games, moves that had little to do with platoon splits. They faced one lefty starter during the series, Framber Valdez, and had righty Harrison Bader lead off that game, but Bader also led off in Game 4 against fellow righty Lance McCullers Jr.; lefty Anthony Rizzo and righty Gleyber Torres led off the other two games against right-handers. The Yankees also had three different starting shortstops in the series.

Aside from the Yankees’ antics, there are also generally more in-game offensive substitutions in the playoffs. Below are the number of position players used per team per game over the last five years:

If anything, these extra alterations might detract from a team’s chances due to the pinch-hitter penalty and perhaps even an analogous one for substitute defenders. But the playoffs are a crapshoot, and from the perspective of a team, it feels good to be proactive when a title is on the line even if said proactivity doesn’t change a thing. In such a short series, especially relative to a long regular season, making changes like these may appease the worries of the front office and fanbase more than anything else.

These kinds of moves aren’t relegated to the offensive side, either. As my colleague Jay Jaffe pointed out, teams have used more pitchers per game in the postseason than the regular season for each of the past eight years. According to his analysis, in this case, more pitching substitutions do lead to more team success: relievers consistently outpitch starters on a per-inning basis, perhaps even more so in the postseason.

Why, then, do teams often opt to keep their fourth and/or fifth starters on their playoff rosters to use in relief?

Traditional baseball maxim holds that starters’ stuff will play up in relief; namely, their velocity will increase. Further, fourth and fifth starters are often relegated to the back of the rotation, failing to make the leap to the front, when they struggle against opposite-handed hitters. Deploying such pitchers out of the pen can make it easier for them to enjoy a platoon advantage. Multiple studies back up this conventional wisdom. Pitchers who traverse both roles typically have lower ERAs, higher strikeout rates, lower home run rates, lower wOBAs, and lower BABIPs as relievers.

That sounds great, right? Starters are worse than relievers on a per-inning basis when the former toss multiple innings per outing, but once starters move to shorter stints, the discrepancy should fall away as their stuff plays up and they garner more favorable matchups. However, as with any move to a new role after a long season in a different one, there is some risk involved.

A Beyond the Box Score study back in 2015 used the fourth/fifth starter move to the postseason pen to approximate how much a typical starter’s stuff will play up as they move to relief. They found that, when weighted to account for changes in offensive quality between the regular season and playoffs, these pitchers allowed fewer runs without a meaningful change in strikeouts and with an increase in walks, which doesn’t really make sense from a fielding-independent pitching standpoint. Keep in mind that we are working with crapshoot samples here, but numbers can be so egregious that you can’t help but take notice. And that’s what happened to me when I compiled statistics for these pitchers in this postseason.

The eye test is what gave me inspiration. Corey Kluber lost Game 2 of the Wild Card Series for the Rays in the 15th inning by allowing an Oscar Gonzalez home run. In the Division Series, a walk-off bomb off the bat of Yordan Alvarez rendered Robbie Ray the Game 1 loser in relief. In the Championship Series, a Jeremy Peña home run off of Frankie Montas provided the Astros with an insurance run in Game 1. And finally, in Game 1 of the World Series, Luis Garcia gave up a go-ahead solo shot to J.T. Realmuto in the 10th.

My target was slightly different than that of the aforementioned studies. I was only interested in pitchers who primarily started games (i.e., more than half of their appearances were starts) in the regular season, and I was only interested in their postseason outings that were shorter than two innings (i.e., outings whose primary purpose was to provide relief). The results were as follows:

On a per-inning basis, these pitchers have fared far worse in these outings than they did as starters during the regular season. While the strikeout and walk numbers aren’t all that different, they have allowed far more hits and home runs, leading to a very bloated ERA.

In small samples, home runs and hits can be volatile due to finnicky BABIPs and home run-to-fly ball rates. So there is definitely some poor fortune at play here. But the stuff isn’t really playing up either, as evidenced by the lack of substantial change in strikeout and walk rate. This could just be due to the stiffer competition come October, but it’s also hard to ignore an ERA difference of nearly two runs.

Writ large, these numbers call into question whether it’s worth using backend rotation types at all in the playoffs if they aren’t going to start. Perhaps it would even be more beneficial for a team to use its best Triple-A relievers, who are used to short stints and might just be better in them than these fourth and fifth starters. On the flip side, if the trend away from starting pitchers on short rest continues — only Nestor Cortes Jr. has gone more than three innings on three days rest or less in these playoffs — teams can continue to make an argument to roster backend starters in case their aces need an extra day.