Baseball Toaster was unplugged on February 4, 2009.
Christian's questions at the A-B site regarding left-handed pitching got me to thinking a bit, and that's got to be dangerous.
I had looked at the percentage of games started by lefties and found that it was it's lowest ebb since the 1930s:
| Decade | Avg LHP GS % |
|---|---|
| 1870s | 18.33% |
| 1880s | 21.20% |
| 1890s | 20.14% |
| 1900s | 22.05% |
| 1910s | 25.88% |
| 1920s | 26.55% |
| 1930s | 23.53% |
| 1940s | 25.06% |
| 1950s | 29.52% |
| 1960s | 31.43% |
| 1970s | 31.86% |
| 1980s | 31.67% |
| 1990s | 28.72% |
| 2000s | 24.97% |
So where have all the lefties gone? I thought that maybe they moved to the bullpen as the significance of middle relief increased to work more and more as situational pitchers. To test this theory I built a table per decade of the percentage of left-handed innings pitched, relief appearances, pitcher-years (i.e., cumulative number of pitchers for each year in a decade). Here are the results:
| Decade | %IP | %RA | %Total # |
| 1870s | 3.30% | 9.15% | 7.66% |
| 1880s | 14.63% | 12.83% | 15.24% |
| 1890s | 17.60% | 17.82% | 20.93% |
| 1900s | 21.46% | 20.38% | 23.95% |
| 1910s | 25.39% | 25.27% | 26.08% |
| 1920s | 26.46% | 27.78% | 27.96% |
| 1930s | 22.93% | 22.20% | 23.56% |
| 1940s | 23.97% | 21.47% | 24.45% |
| 1950s | 27.83% | 24.06% | 27.79% |
| 1960s | 29.24% | 26.47% | 29.90% |
| 1970s | 31.49% | 32.73% | 31.60% |
| 1980s | 31.05% | 33.06% | 31.24% |
| 1990s | 28.24% | 31.99% | 29.97% |
| 2000s | 25.15% | 30.19% | 27.30% |
You'll note that the number of relief appearances remains high (over 30%) since the '70s. However, the percentage of innings pitched and pitcher-years has decrease in the last decade and one-half.
So why the change? Did lefties go out of vogue? Perhaps lefties as a whole were being less successful of late. Perhaps the lefty-lefty advantage was diminishing. I thought that looking at the ratio of lefty ERA to average ERA would be telling:
| Decade | LHP ERA | ERA | LHP ERA to avg | %Diff |
| 1870s | 4.01 | 2.82 | 141.86% | |
| 1880s | 3.38 | 3.29 | 102.76% | -27.56% |
| 1890s | 4.23 | 4.09 | 103.51% | 0.73% |
| 1900s | 2.80 | 2.84 | 98.76% | -4.59% |
| 1910s | 2.88 | 2.96 | 97.47% | -1.30% |
| 1920s | 4.03 | 4.03 | 99.92% | 2.51% |
| 1930s | 4.20 | 4.28 | 98.26% | -1.66% |
| 1940s | 3.72 | 3.75 | 99.25% | 1.01% |
| 1950s | 3.91 | 3.97 | 98.44% | -0.82% |
| 1960s | 3.51 | 3.56 | 98.42% | -0.02% |
| 1970s | 3.63 | 3.70 | 98.29% | -0.13% |
| 1980s | 3.85 | 3.87 | 99.67% | 1.40% |
| 1990s | 4.29 | 4.29 | 100.18% | 0.51% |
| 2000s | 4.45 | 4.47 | 99.57% | -0.61% |
Could it be that the 1.40% increase in the Eighties has caused left-handers to fall out of favor? It is interesting to see that by the turn of the last century, lefties outperformed righties according to ERA and that was in effect until the 1990s.
Let's take a look from another point of view. What do Pitching Win Shares have to say in the matter? I took the total pitching win shares and total innings pitched for lefties and all pitchers and divided them to get PWS per IP. I then represented the lefty value as a percentage of the whole:
| Decade | LHP WS/IP | Overall | % |
| 1870s | 0.0194 | 0.0275 | 70.38% |
| 1880s | 0.0583 | 0.0590 | 98.90% |
| 1890s | 0.0554 | 0.0592 | 93.49% |
| 1900s | 0.0587 | 0.0581 | 101.09% |
| 1910s | 0.0595 | 0.0576 | 103.33% |
| 1920s | 0.0582 | 0.0582 | 100.06% |
| 1930s | 0.0599 | 0.0585 | 102.33% |
| 1940s | 0.0597 | 0.0583 | 102.38% |
| 1950s | 0.0597 | 0.0587 | 101.80% |
| 1960s | 0.0589 | 0.0590 | 99.97% |
| 1970s | 0.0596 | 0.0590 | 101.08% |
| 1980s | 0.0588 | 0.0590 | 99.57% |
| 1990s | 0.0570 | 0.0595 | 95.94% |
| 2000s | 0.0551 | 0.0564 | 97.71% |
Again it wasn't until the 1900s that lefties played a significant role on a staff. And as the relief era dawned (1960s) relievers were either used much less or were much less successful. Given that ERAs for lefties were still dropping faster than the overall ERAs, I would think that they were just being used less often. The 1990s experienced an abrupt dropoff in lefty Win Shares. Then they started to increase in the last half decade.
Could it be that lefties are being moved from starters to closers:
| Decade | %Sv |
| 1870s | 1.92% |
| 1880s | 9.70% |
| 1890s | 14.59% |
| 1900s | 16.10% |
| 1910s | 24.94% |
| 1920s | 25.04% |
| 1930s | 21.05% |
| 1940s | 18.93% |
| 1950s | 21.04% |
| 1960s | 23.29% |
| 1970s | 30.48% |
| 1980s | 26.43% |
| 1990s | 18.64% |
| 2000s | 11.41% |
Well, that's not the case. Maybe we should look at the number of closers (20+ saves per year):
| Decade | %20 Sv |
| 1920s | 0.00% |
| 1940s | 100.00% |
| 1950s | 0.00% |
| 1960s | 15.56% |
| 1970s | 33.78% |
| 1980s | 21.99% |
| 1990s | 15.12% |
| 2000s | 7.07% |
OK, they don’t seem to be closers now, and they aren't all being used as middle relievers; otherwise the percentage of the total number of relief appearances, although it is still high, would be increasing nit decreasing.
Therefore, my theory is that lefties are indeed being used less often today because of diminished returns of the lefty-lefty advantage. If we had historic lefty-righty splits, then we could test that theory. So it'll have to remain a theory based on the circumstantial remnants of proof found in the statistical record).
[By the way, the quote's from Barney Rubble.]
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