Saturday, December 10, 2022
Improving WAR: Relief Pitcher Roles
When is a relief pitcher not a relief pitcher?
Background
Pitcher roles cannot be split into just two, starter and reliever. At most, you can say starter and not-starter. But that not-starter role is really a catch-all for all kinds of pitchers. And even starter, with the advent of The Opener, no longer actually applies.
If a reliever enters a game in the 9th inning, he has an expectation of really only pitching one inning. When a pitcher knows, or expects, to only get three outs, he's going to approach each batter much differently. If a reliever enters the game early, his expectation, and it's likely an explicit instruction from the manager, is that they'll have to pitch at least two innings, if not more.
We already learned from The Book that a pitcher that enters the game as a relief pitcher will have a wOBA some 25 or 30 points better than if that same pitcher enters the game as a starting pitcher. A starting pitcher is pitching with one hand tied behind his back, while the reliever is not so entangled. So, no surprise in terms of direction, but we learned about the magnitude. I've never looked to see how a relief pitcher performs based on when he enters the game. Until now.
Game Entry
Let's first see if what we believe to be true is true: a relief pitcher that enters the game early will pitch longer than if he enters the game late. Well, we know it's true. The real question is not if something is true, but the extent of how much its true. Most of the time, we don't care about the existence of something, but the magnitude of that existence. Platoon advantage is real. How big is it? Pretty big, since it's so easy to find. Clutch is real. How big? Not that big, it's really hard to find it. So, we don't care about proving if it exists. We care about how big it is.
For each relief appearance since 2010, limited to the top of the inning, I tracked the inning the reliever entered the game, as well as how many outs he recorded that game. Here is the average number of outs recorded by relief pitchers, based on when they entered the game. That 10 means any extra inning.
There's no surprise in terms of direction, but we finally learned of the magnitude. Entering the game in the first four innings, but especially the first three, and there's an expectation of needing to average more than six outs a game. So, these relief pitchers are really long relief pitchers. Once a pitcher enters the game in the fifth inning, but especially by the sixth inning, relief pitchers have a much shorter outing, averaging under four outs per game.
One technical note: because some games were scheduled for 7 innings, those games were adjusted by adding-2 to each inning. Entering the game in the 6th inning of such games is equivalent to entering the 8th inning of a 9 inning game. A bit annoying, but better to do that than to represent the data as innings-left-in-game, which is not an obvious point of view.
Game Performance
Ok, now we know the expectations of relievers based on the inning of entry. Does their performance follow based on what we've learned in the past, that the shorter the outing, the better the performance? Yes! I guess I should say yes, since we shouldn't get excited about seeing something that we expected to see. We're doing all this to learn about the magnitude of its existence.
So, how much does performance degrade in longer outings?
Since the quality of pitchers differ based on the inning they enter the game, we need to know their career performance level as a baseline. So, you will see two lines, one is the performance of the pitcher that game, and the other is the career performance of that pitcher EXCEPT for the game.
Yes! We not only see the expected gap between performance level and expected performance level, we also see it concentrated in the first four innings, exactly when we expected to see that gap. The early-inning relievers are expected to be long-relievers and so need to pace themselves. While not as much pacing as a starting pitcher, it lands somewhere between there and late-inning or short-relievers. How much is that gap? 9 points in wOBA, or about one third of the distance from short-relievers to starting pitchers.
We also get a surprise: the extra inning reliever. A relief pitcher that enters the game in the top of extra innings won't necessarily be pitching all-out, like the late-inning short-relievers. There's probably a couple of reasons for this. The first is that coming into the top of the 10th or later, this means there's a good chance that the game will go one more inning. The second is that the manager may be going deep into his bullpen, and so those pitchers may not have been even expected to pitch that game. The gap we see is 11 points in wOBA, in-line with the early-inning long relievers.
So, an argument can be made that we have two kinds of relievers: those that enter during regular play starting in the fifth inning, and those that enter before the fifth or extra innings. When we evaluate relief pitchers, we need to be made aware of which kind of relief pitcher they were that game.
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