## A Magic Number to Increase Your Odds of Winning

Dilip Vishwanat

There are so many numbers in baseball that it can seem overwhelming but there's actually one number in particular that is a good determinant as to whether your team will win or not and at what rate.

There are many different ways to go about trying to win a baseball game, but there is still only one way to guarantee it and that is to score more runs than your opponent. Some teams rely on a powerful offense to get the job done while others rely on strong pitching and defense. No two games are ever the same, and neither are any two wins. Different events during the course of a game shape the immediate and future outcome as well as the strategies employed by each team.

But what if there was a way to place the odds forever in your favor? I’m not saying that it would guarantee anything but at the very least increase your odds of winning. Joe Lemire from Sports Illustrated wrote a piece a while back detailing this very thing. He calls it baseball’s magic number but I like to look at it as the Rule of 39.

What's so magical about 39? It's frequently the dividing line between winning and losing.

First, some background: As a major league pitching coach, Rick Peterson always clutched a series of index cards, on which he had written matchup data for his relievers facing opposing hitters.

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Peterson, now the Orioles' director of pitching development, previously was a big league pitching coach for the Athletics, Mets and Brewers, and it was during his time in Oakland that he had this revelation.

--snip--

Peterson asked the team's analytics department to research the correlation of winning percentage with the number of batters faced in a game. That research, he said, found a tipping point between 38 and 39 batters faced.

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Here's why: Since 1991 home teams that have faced fewer than 39 opposing batters in a nine-inning game -- four full times through the lineup, plus three additional hitters -- win roughly three-quarters of the time (74 percent) while teams that have faced 39 or more hitters have won only 31 percent of games.

Moreover, in the last 22 seasons home teams that have faced 39 opposing hitters have won almost exactly 50 percent of their games -- 50.082 percent, to be more precise -- making 39 the inflection point of winning or losing.

The following table was also created by Lemire for his work on this subject.

Winning Percentage As Correlated With Batters Faced

1991-2012

 Batters Faced Winning Percentage Batters Faced Winning Percentage 27 100.0 41 36.2 28 97.4 42 31.2 29 96.4 43 23.4 30 95.2 44 21.9 31 93.2 45 17.4 32 89.2 46 12.6 33 87.0 47 11.2 34 82.1 48 6.7 35 77.0 49 7.5 36 69.4 50 3.0 37 65.2 51 5.7 38 57.4 52+ 2.4 39 50.1 Summary 27-38 74.3 40 44.7 Summary 39+ 31.0

(An important note on methodology: Peterson's original data could not be obtained, so it's been mimicked here as best as possible. Data was studied only for home teams in nine-inning games in order to guarantee that the club got 27 outs, permitting an apples-to-apples comparison of only games in which a pitching staff got the same number of outs.)

I don’t doubt that this holds true over the course of a season for all teams in major league baseball but what I would like to know is what the best way to get there is. I decided to take a look at data for starting and relief pitchers from 1991-2012 to determine how many hitters, on average, they were facing and how many innings, on average, they were pitching per game.

Starting pitchers started a total of 102,138 games, pitched a total of 607,412.2 innings, and faced a total of 2,619,503 batters. That means they averaged nearly six innings per start (the average came out to 5.95 so it’s between 5.2 and 6 IP) and faced 25.65 batters per start. That still leaves the bullpen with three innings to cover and they would have to face no more than 14 hitters to give their team at least a 50.1% chance of winning that game based on the research above.

Relief pitchers during this same time period appeared in a total of 268,817 games, pitched 304,235 innings, and faced 1,320,825 batters. That means the average relief pitching appearance lasted between one and one and a third innings and they faced an average of 4.9 batters per appearance. Those numbers actually kick their team’s winning percentage below 50.1% according to the data. The combination and methods in which starters and relievers are being used just isn’t getting the job done. Obviously some teams are better equipped for this than others but is there a way for everyone to do better?

Would only allowing starters to pitch three innings per start before removing them for the bullpen help get it done? My reasoning for that is based on the fact that opposing hitters had a .250/.310/.399 batting line against starters who only saw that starter once in a game (according to Baseball Reference). It would, technically, be considered a radical move by any team that tried it but would it actually work?

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