Scott’s Miscellany – Reliever Rest

The title of the article is an allusion to Schott’s Miscellany, which you should definitely check out if you never have and feel compelled to know that a group of larks is called an exaltation or that a member of the 32nd degree of Freemasonry is known as a Sublime Prince of the Royal Secret.

–Reliever Rest–

The public debate of reliever usage tends to center on situational leverage, platoon advantage, and decision-making tied to the save statistic’s criteria. What is less discussed is reliever availability. We all have a vague notion that relievers who have pitched a lot recently are more likely to be given rest, even if the specifics of a game would otherwise warrant them pitching. I was curious if historical trends in usage could make that vague notion more concrete.

There are a lot of angles to potentially tackle that question, so I started with the most basic one I could think of. Assuming that a reliever threw X pitches in a game today and that his team plays again tomorrow, how likely is he to pitch that next day? It turns out, that trend was very clear.

From 2002-2014, the number of pitches thrown in a game one day correlates extremely well with the likelihood that a reliever pitches again in a game the next day. A simplified formula for that likelihood is:

.40 – Pitches / 120

Even a reliever who throws just one pitch in a game will most likely not be used the next day. Sometimes, that reliever will have pitched on consecutive days. Sometimes, the next day’s starter lasts deep into the game. Sometimes, the situations in that next game do not match that reliever’s skill or usage pattern. That establishes the intercept at around a 40 percent chance that a reliever will be used the next day. From there, there is a clear linear trend of the more pitches thrown, the less likely a reliever will pitch the next day.

Based on the formula, here are the least and most likely fantasy-relevant relievers to pitch on Thursday:

Wade Davis and Steve Cishek are the two fantasy-relevant relievers who eclipsed 20 pitches yesterday and whose teams have a game today, and they are projected to have only a 22 percent chance of pitching today. The limited Thursday slate removes some of the more extreme cases. For instance, Dellin Betances was well clear of his peers with 28 pitches, but the Yankees have an off day.