THE BOOK--Playing The Percentages In Baseball

Tuesday, October 18, 2011

Summarizing late inning starter and reliever performance…

I realize that lots of people have chimed in or lurked a little with regard to the data presented about starters and relievers pitching in the later innings, especially the 9th, and that the data can be confusing.  In an effort to summarize an analysis of the data, here is what it suggests:

If managers and coaches can tell whether a starting pitcher is “on” in any given day based on how he has pitched in the early and middle innings, we should see gradually increasing performance in the later innings, relative to a starter’s overall performance.  IOW, if we look at all starters who pitch the 7th, we should see a collective excellent performance in 1-6 (otherwise they would not be allowed to continue).  We do.  We see a wOBA against of .322 (23 points better than their seasonal wOBA) in innings 1-6 (and presumably a low pitch count and few runs allowed) when they are allowed to start the 7th.  Presumably their managers and coaches are thinking or saying, “He is pitching well, and his stuff is good today.  We’ll let him start the 7th - at least.”

Since a pitcher’s overall wOBA against is a combination of days when his stuff is good and his stuff is bad, we should see better than average performance in inning 7.  We see, however, a wOBA against of .354 while these pitchers’ overall wOBA is .345, which is almost exactly what we would expect the 3rd time through the order.

So it seems that managers and coaches are not able to tell that their stuff is good that day and they will continue to pitch particularly well, since they don’t.  In fact, if they had let these pitchers pitch the 7th when they were pitching horribly in 1-6, they would have had to pitch the same in the 7th as they did when they were pitching exceptionally well in 1-6, since the two samples have to average to their overall seasonal numbers.  IOW, if they are overall .345 and they pitch at .354 the third time through the order in the 7th, when they have been pitching great in 1-6, they have to also pitch at .354 when they are pitching badly in 1-6, since we expect .354 overall!

For inning 8, we should see the same phenomenon but even stronger.  Since pitch counts are higher and short relievers are now readily available, we should see a manager only let his starter start the 8th when he has pitched even better in 1-7 and the manager believes that he is really “on” that day.  He has to be even more “on” than in the 7th inning since his pitch count is higher and short relievers can now come in to pitch.  In fact, going into the 8th inning, these pitchers who are allowed to pitch the 8th have pitched at a .297 level in innings 1-7!  Surely they are “on”!  So we expect his 8th inning performance to be really better than their overall performance.  While it is true that these guys who are allowed to pitch the 8th have been even better in 1-7 than pitchers who were allowed to pitch the 7th, it turns out that in inning 8, these guys once again, like the 7th, pitch at their expected seasonal levels.  They were at .345 in the 8th and they were .343 pitchers overall.  Again, given that they were pitching the 3rd or 4th time through the order, that is about what we would expect, if there were no predictive value associated with their prior innings.  Remember these numbers, like the .345, are adjusted for the pool of batters in that inning.

Once again, managers simply cannot tell whether their starters are “on” or not, or perhaps there is no such thing as being “on.”

What about inning 9?  Again, we should see the same phenomenon, but even stronger than inning 7 and 8.  Pitchers who are allowed to pitch the 9th pitched at .283 in 1-8.  This time we do see better than expected pitching in the 9th!  Starters who pitch the 9th not only show exceptional performance in 1-8, but they continue to some extent that exceptional performance in the 9th.  They are .330 in the 9th even though they are .342 pitchers overall.  They do around 13 points better than expected (the 4th time through the order, pitchers typically do 1 point worse than overall).  How can they all of a sudden do that in the 9th but not at all in the 8th or the 7th?  Surely managers just don’t let any starter pitch the 7th and 8th yet all of a sudden they decide that only starters who are “on” that day will pitch the 9th?  That makes no sense!

So what is the explanation?  It is simple once we look at how wOBA is recorded in different score situations (whether the batting team is tied, up by a little, up by a lot, down by a little, or down by a lot).  As it turns out, even if the actual quality of the pitching (and hitting) is the same, the wOBA can change radically because of the approach of the batters, pitchers, and fielders, depending on the score in the 9th (or later) inning only and because the wOBA weights are based on average values (across all innings) of the various events.  In fact, we see that for all pitchers in the 9th, including relievers, who actually pitch an overwhelming majority of 9th innings of course, wOBA is much lower when the pitching team is ahead by 2 or more runs, and much higher when the game is tied or the pitching team is ahead by only one run or is losing.  This is evident from looking only at the relievers, who aren’t pitching the 9th inning because they are “on” that day.  They are pitching the 9th because they are primarily closers or late inning relievers in general.  And please remember, when I say that wOBA is lower in games where the pitching team is ahead by a lot and higher when the game is close or they are losing, I mean relative to the pool of batters and the quality of the pitchers in that “bucket.”

So, for example, if in blowouts, the average pitcher (reliever and starter) is a .350 pitcher and the batters are average, then we might see a wOBA of .330 (20 points lower than expected).  If in close games, the average pitcher is a .320 (again, with average batters), we might see a wOBA of .340, 20 points higher than expected.

Here are the numbers in the 9th inning for all pitchers based on score differential of the pitching team.  I’ll only use score differentials when the pitching team is winning so we can use home and road numbers (the numbers for when the pitching team is losing are similar to when the game is close).  Look at the pattern.  It is obvious.  The first number is the wOBA adjusted for the batting pool. The numbers in parentheses are the seasonal talent levels of the pool of pitchers in that bucket.  Remember these numbers are for all pitchers, which are mostly relievers of course, since 90% or so of all PA in the 9th inning are pitched by relievers.

Up 4 or more runs: .325 (.337)
Up 3: .305 (.318)
Up 2: .304 (.318)
Up 1: .318 (.317)
Tied: .356 (.330)

When up by 2 or more runs, wOBA for all pitchers is around 13 points lower than “expected” (seasonal numbers).
When up by 1, it is 1 point higher.
When tied, it is 26 points higher!

So that still doesn’t explain why all of a sudden in the 9th inning, we see starters doing exceptionally well.  It does if you know this one important fact:  Most of the time that a starter pitches in the 9th, he is pitching with a large lead.  In fact, 76% of the time that a starter pitches in the 9th his team is ahead by 2 runs or more.  55% of the time, his team is ahead by 4 or more runs.  Only 9% of the time that a starter pitches in the 9th is the game tied, which is when wOBA is the highest by far, for all pitchers.

Contrast that to relievers.  Only 48% of the time do they pitch with a 2 or more run lead, 27% of the time their team has a 4 or more run lead, and 13% of the time they pitch when the game is tied.  They also pitch considerably more often than starters when their team is losing, The wOBA is also quite high in games (in the 9th of course) in which the pitching team is losing.

And that is why starters seems to pitch so well in the 9th. It is not that they are really pitching well. It is just that the way wOBA is figured it understates what is really happening (the weights of the events are not correct, and other things probably occur more often, like sac bunts and IBBs) in the 9th inning of games in which starters tend to pitch (close games, not losing) presumably because of the approach of the batters, fielders, and pitchers.  Again, we know that the low wOBA against for starters in the 9th has nothing to do with the starting pitchers themselves because we see that when the pitching team is ahead by a lot with a reliever in the game, the wOBA is just as low.  Again, it is just that starters tend to pitch in the 9th when they are leading by 2 or more and relievers tend to pitch the 9th when their teams are losing or the game is close.

In fact, when we look at games in which the score is close, the starters’ wOBA against is around the same as the relievers (relative to their overall wOBA against) and when the pitching team is ahead by a lot, the starters’ wOBA against is also the same as the relievers’.  No difference.  Starters and relievers pitch the same in the 9th relative to their true talent.  Starters do not pitch well despite having pitched exceptionally well in innings 1-8.

A simple but perfectly apt analogy would be this:

Let’s say that during the day wOBA was 10 points higher than at night, given the same pool of batters.  And let’s say that pitchers with blond hair pitched mostly at night and pitchers with brown or black hair pitched mostly during the day.  What would we find?  We would find that blond haired pitchers appeared to pitch a lot better (by almost 10 points) than dark haired pitchers.  This would be an illusion.  We would find of course that blonds during the day pitched the same as brunettes during the day and that both groups also pitched the same at night.

In this case, starters are blondes and relievers are brunettes and night games are games in which the pitching team is ahead by a lot and day games are games in which the score is close or the pitching team is losing.

So, there does NOT appear to be any predictive value to pitchers who have pitched great in 1-6 or 1-7 or 1-8 AND their manager considering them to be “on” that day (I presume) and thus leaving them in the game.  We only saw that in the 9th inning anyway, and it was an illusion created by the fact that starters tend to pitch when they are ahead by a lot and ANY pitcher will have a low wOBA against, presumably because of a non-typical approach by batters, pitchers, and fielders, and relievers tend to pitch in closer games (or losing games) when ANY pitcher will have a high wOBA against, again, presumably because of a non-typical approach by batters, pitchers, and fielders.

I hope I have explained this well…