02 November 2007

How long are extra-inning games?

From the Baseball Reference Stat of the Day: the number of Major League Baseball games which went exactly n innings this year are as follows:



n1011121314151617
number of n-inning games975834169312

(The table in the original post actually gives twice the number of games which have gone at least n innings; I've done the obvious manipulations to get this table.)
If you look at this sequence, one thing that sticks out is that it's roughly geometric. Each number is just about half the number before. What this indicates is that a game has roughly the same probability of ending in any extra inning, namely about one-half. The geometric distribution is "memoryless"; this indicates that at the beginning of the nth inning, for any n ≥ 10, the probability of the game going one more inning is 1/2, two more innings 1/4, three more innings 1/8, and so on. The expected number of additional innings to be played is always the same -- around two.

This isn't all that surprising -- every extra inning "looks the same" when it starts. It wouldn't surprise me to see that things start to change, say, around the fifteenth or sixteenth inning when teams just run out of pitchers -- it wouldn't surprise me to learn that scoring rates go up in, say, the seventeenth inning because whoever is on the mound either is the guy you never let play or the guy who usually pitches an inning or two that's in his fifth inning of work -- but there's not enough data from just a single season to say anything for sure.

But if we look a bit closer at the data, it does look like something like that happens. To be somewhat more precise, there were 220 extra-inning games played this year, and 465 extra innings; thus at the beginning of the tenth, one should expect a game to go 2.11 more innings. There were 123 11-inning-or-more games played this year, and 245 innings numbered 11 or higher; thus at the beginning of the eleventh a game should go 1.99 more innings. Similar numbers for the beginning of the twelfth, ..., seventeenth are 1.88, 1.84, 1.73, 1.83, 1.67, 1.00. The distribution isn't quite geometric, and the expected number of innings remaining in an extra-inning game actually does decrease as time goes on.

(Also, in general the fifth and sixth innings are surprisingly high-scoring. I blame the fact that starters seem to fall apart a lot in the fifth or sixth these days. I'm not saying I could do better, but these guys make a hundred times what I do, so they should be held to higher standards.)

I actually saw this in action on July 25th, when the Phillies played the Nationals and won in fourteen innings, of which I only saw the first nine. My father and I went to the game, and I believe my father had never left a baseball game early in his life. But we left after the ninth, because we had to pick my mother up at the train station. She said that she wouldn't have minded waiting, say, an inning or so. But you never know how long the game is going to last, which is why we left... and if we had stayed around for the rest of the game she would have been waiting at the train station for two hours. You always think the game will end soon. And it usually will. But sometimes it doesn't.

7 comments:

Anonymous said...

The table is titled "number of games lasting exactly n innings" and the commentary states that the table actually is twice the number of games lasting at least n innings?

Why are you wasting readers' time with such sloppy garbage? If you can't be precise or clear, don't make a blog.

Isabel said...

anonymous,

the table I adapted the data from gave twice the number of games lasting at least n innings; I'm explaining why the numbers in my table are not the numbers in the original.

Anonymous said...

Just a note to say that I enjoyed the article and understood exactly what you meant about the table. That guy above was a bit of a dick, eh?

~ a different anonymous

Andy said...

I'm the author of the original piece at baseball-reference.com, and Isabel interpreted the data exactly correctly, and has done a very nice analysis here. The reason that my original table listed 2X the number of games is that it looked at EACH team's scoring by inning. Therefore, each game was counted twice in the overall totals.

michael Cassidy said...

Pitchers no longer are required to last beyond 5-6 innings, and like any athlete they would lose confidence in their ability to do go beyond the 5th inning, and I wouldn't be surprised that they habve lost some ability.

To run a marathon you need to train for a marathon not a mile; they would need to go beyond 5 or 6 innings more often.

It would be hard though to convince managers to not change pitchers at the 5th or 6th inning and bring a fresh pitcher in so that the batters would have to adjust.

Anonymous one you have a lot of courage to lecture Isabel about math or baseball; it would be more sensible to learn to read and come back and read what she wrot.e

Anonymous said...

Along with Phil Lowry, I wrote an article about the question of how long extra inning games will last using a model of scoring which we put together. The article was accepted by Mathematics Magazine and will appear before too long, though I would be happy to email a copy to anyone who is interested. Just drop me a note at dglass at gettysburg dot edu

- darren

Michael Cassidy said...

I'd like to read the article.