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Innings histogram for 2009 (Part 1)

Posted by Andy on January 8, 2010

Raphy's recent post about starting pitcher performance in 2009 touched on something I've been thinking about for a while. I did some additional research and have a two-part post looking at the results.

First, here is a plot showing how many innings were pitched in each start in 2009.

I generated this data by using the PI, simply looking up total number of games by the starting pitcher for each number of innings. Keep in mind this covers 2009 only.

Tomorrow I am going to break out the data in the above graph by AL and NL starts. For today, though, let's just look at the above data.

Here are some of the interesting things you can conclude from the data:

  • The average starting pitcher went a little under 6 innings, with exactly 6 innings being the single-most common number of innings pitched. You can figure the exact average number of innings per start by looking at the 2009 pitching splits by role, which shows that in 4860 starts, starters totaled 28257.1 innings, or 5.81 innings per start.
  • Starters were much more likely to pitch an even number of innings, especially later in the game. This can be seen from the high spikes at exactly 4, 5, 6, 7, and 8 IP, as opposed to the much lower numbers in between. This makes a lot of sense for a few reasons. Firstly, it's quite customary to take a pitcher out between innings, especially if looks tired or has reached a high pitch count. Secondly, in the NL, starting pitchers often come out for a pinch-hitter when their turn at bat comes. Thirdly, it seems to be more and more common for managers to use their bullpen in fairly rigidly defined ways, particularly using one reliever as the 7th-inning setup guy, another as the 8th-inning setup guy, and a 9th-inning closer.
  • There's an interesting trend in these later innings. A total of 233 starters were pulled during the 4th inning, meaning with 1 or 2 outs in the 4th. However, 685 starters went a full 5 innings. That means pitchers were 2.94 times as likely to pitch 5 innings than they were to get pulled during the 4th. Moving one inning later, pitchers were only 2.54 times as likely to pitch 6 innings than they were to get pulled during the 5th. Advancing another inning, the ratio is 2.36 times as likely to go 7 instead of 6.1 or 6.2. The ratio falls all the way to 1.74 for likelihood of going 8 full instead of 7.1 or 7.2 This all makes sense--the later the game gets, the more likely that the starter gets pulled in a critical situation. However, once a starter gets into the 9th inning--meaning 8.1 or 8.2 IP, he's 5.73 times as likely to pitch the full 9 innings than to get pulled at that point. This follows intuitively--if a manager has made the decision to let the starter pitch the 9th inning, most of the time he finishes it, often I would assume because his team has a comfortable lead. Keep in mind that if the starter gives up a baserunner or two to start the 9th but doesn't record an out, such an occurrence is invisible in this study because that counts as 8 IP.
  • Also of note is that there isn't much difference in the odds that a starter gets taken out with 1 vs. 2 outs in the inning. You can tell this since the data points for 5.1 and 5.2 are pretty similar, or 6.1 and 6.2, etc. This makes sense since the starter is likely to get pulled for two reasons: either he's gotten in trouble, which is pretty much just as likely to happen with one out as with two outs, or a special matchup has arisen, such as a tough lefty, for whom the manager wants to put in a lefty specialist reliever. This, too, is equally likely to occur with any number of outs in the inning.

In Part 2, we'll look at the difference in this graph in the AL vs. the NL, which I found quite interesting.

6 Responses to “Innings histogram for 2009 (Part 1)”

  1. apreziosi Says:

    Interesting stuff. Especially the even-number innings numbers. Although you cite that "there isn't much difference in the odds that a starter gets taken out with 1 vs. 2 outs in the inning" I'd submit that those numbers are at least partially the responsibility of the bullpen. The runners left on would be charged to the starter if the reliever let them in, so the even-numberd innings are your most valid numbers for evaluating the starter.
    It's kind of depressing (and telling of the current state of the game) that starters are barely lasting 6 innings. For the money they make you'd think they'd pitch further into games. High-salaried starters are giving over control of a game to 2 or possibly 3 pitchers.

  2. JohnnyTwisto Says:

    And the pitchers who take over for them are high-salaried as well. Let's not make this into some macho thing. There are a lot of conditions which work against starters being able to pitch as long as they used to, and their managers have collectively decided this usage is most effective. Even in 1968, starters lasted all of 6.6 IP/start, and I'm sure people who grew up in the deadball era were lamenting that generation of pampered pansies.

  3. JohnnyTwisto Says:

    I don't think you mentioned it, but I'm certain a big reason for the big jump in completing 5 innings as opposed to 4 is to give the pitcher a chance for a win.

    It would be interesting to track the development of relievers (not just closers) being used for exactly one inning. Some things I looked up a while back made it appear that Cito Gaston may have helped push this ahead with the early '90s Blue Jays, but I've never done any rigorous study (nor am I aware of one).

  4. DoubleDiamond Says:

    Were there any starters who pitched into extra innings in 2009? The graph ends with 9.

  5. statboy Says:

    No one has pitched more than 9 innings in a game since 2007.

  6. Andy Says:

    I just graphed #3, i.e. non-save situation relief appearances of exactly 1 inning, and the results are absolutely shocking. I will post it on Monday, but here's a tease. In the 1950s and 1960s, about 22-23% of all non-save relief appearances were 1 inning. In the 1970s and 1980s, it fell to about 20-21%. Starting in the mid 1980s it has steadily risen linearly and is now at...wait for it....FORTY-FIVE PERCENT.