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June 28, 2000

Doctoring the Numbers

Where Have All the Southpaws Gone?

by Rany Jazayerli

One of the most striking changes to the landscape of major-league baseball has been the disappearance of the left-handed starting pitcher. In the American League, left-handers made fewer than 20% of all starts last year, allowing teams like the A's to take advantage by stacking their lineup with left-handed hitters.

How dramatic is the decline? Here is a list of the percentage of starts made by left-handers in the AL over the last five years:

Year  Lg   LHP   RHP     LH%

1999 AL 449 1816 19.8% 1998 AL 608 1674 26.6% 1997 AL 643 1621 28.4% 1996 AL 651 1615 28.7% 1995 AL 622 1403 30.7%

Teams were more than 35% less likely to face a left-handed starter in the AL in 1999 than they were in 1995. But compare that to the National League:

Year  Lg   LHP   RHP     LH%

1999 NL 697 1894 26.9% 1998 NL 670 1940 25.7% 1997 NL 548 1720 24.2% 1996 NL 524 1744 23.1% 1995 NL 566 1448 28.1%

Between 1995 and 1996, the percentage of left-handers dropped precipitously, but southpaws have actually made a higher percentage of starts each year since.

Is the number of left-handed pitchers at a historic low in the American League? Not even close. The 1999 AL ranks just 24th on the list of the most right-handed leagues this century. The four most right-handed leagues were the 1902-03-04-05 NL, a span of time in which just 661 of 4679 starts (14.1%) were made by left-handers. (In the AL during the same four years, lefties made 25.5% of starts.)

For the 19th century as a whole, left-handers made just 13.2% of all starts.

But while left-handers are not at their lowest point ever, they are rarer than they have been in more than half a century. Here are the overall percentage of starts made by left-handers, broken down in five-year increments:

Years       LH%       Years     LH%

1900-04 20.4% 1950-54 32.7% 1905-09 22.8% 1955-59 26.3% 1910-14 23.7% 1960-64 30.8% 1915-19 27.1% 1965-69 32.0% 1920-24 25.2% 1970-74 32.0% 1925-29 27.5% 1975-79 31.8% 1930-34 25.3% 1980-84 31.1% 1935-39 21.5% 1985-89 32.4% 1940-44 21.7% 1990-94 31.2% 1945-49 28.6% 1995-99 26.2%

The 26.2% of starts made by left-handers between 1995 and 1999 is the lowest total in any half-decade since the 1930s. This comes after a 30-year stretch in which the frequency of starts by left-handers remained remarkably consistent between 31.1 and 32.4 percent.

In what leagues were left-handed starters most common?

Year  Lg   LHP   RHP     LH%

1949 NL 506 738 40.7% 1983 AL 867 1403 38.2% 1950 AL 471 769 38.0% 1990 NL 724 1220 37.2% 1992 NL 721 1223 37.1%

In addition to 1990 and 1992, the 1991 NL (36.2%) ranks ninth all-time. As much as the current dearth of left-handers, it is the relative abundance of them less than ten years ago that makes their decline seem all the more dramatic.

The five most left-handed teams since 1900:

Year   Team            GS by LHP

1983 New York (AL) 127 1975 Chicago (AL) 124 1974 Baltimore 116 1979 Chicago (AL) 116 1982 Kansas City 113

For whatever reason, nine of the ten most left-handed teams played between 1974 and 1983, the lone exception being the 1965 Dodgers. It's not just the longer schedule; if you rank teams by percentage of starts made by lefties, only one earlier team (the 1951 Red Sox) breaks the top ten. (The 1981 Yankees, with 85 of 107 starts made by left-handers, would actually rank first.)

Perhaps the greater question is, "how much difference does it make?" You frequently hear it said that teams can't win without a left-handed starter. No doubt, this stems from the Yankees' historic dominance and the number of great left-handed starters that have toiled for them. But keep in mind that Yankee Stadium has always been a very tough park for right-handed hitters, especially power hitters, particularly before it was redesigned after the 1972 season. Playing in a park that favors left-handed pitching, it isn't surprising that they've had so much success with southpaws.

Let's look at the correlation between the percentage of starts made by a left-hander and a team's overall winning percentage:

LHP%      Teams    WPct.    Yankees    WPct.      Others    WPct.

>=50%       162    .514          16    .556          146     .510
40-50%      272    .511          12    .537          260     .510
30-40%      407    .509          24    .602          383     .504
20-30%      497    .493          20    .591          477     .489
10-20%      333    .496          17    .537          316     .494
<10%        257    .484           8    .533          249     .483

The first two columns show that there is indeed a very strong correlation between the percentage of starts made by left-handers and the team's overall winning percentage. On average, teams who give at least half their team's starts to left-handers have a winning percentage 30 points higher than teams who give less than 10% of their starts to lefties, an advantage of five games over a 162-game season.

But, as the next two columns show, nearly 10% of the 162 most left-handed teams played in the Bronx, while barely 3% of the 257 most right-handed teams were Yankees. The Yankees themselves show little correlation between left-handed pitching and success, but the team's overall success has skewed the numbers slightly. When the Yankees are ignored, we can see that while left-handed pitching still correlates with success, the difference is only about three-quarters as great. Still, an advantage of three or four games a season is not something to be trifled with.

Rany Jazayerli, M.D., can be reached at ranyj@baseballprospectus.com.

Rany Jazayerli is an author of Baseball Prospectus. 
Click here to see Rany's other articles. You can contact Rany by clicking here

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