The last fifteen years have, for a number of reasons been record setting years for offense as career and single season home run records have fallen. Numbers such as 30 home runs or 100 RBIs, which used to be the measure of a very good season, have become less meaningful; ERAs have ballooned; and middle infielders, who used to be in the lineup largely for their defense, are now expected to produce at the plate as well. Other basic numbers provide further evidence of increased offense. In the NL, the lowest ERA of the last 15 years was 4.11 in 1996. Every years from 1954-1993, the league ERA was lower than that. Similarly in the AL, the 4.36 ERA in 2008 and 2005 was the lowest of the last fifteen years, but higher than every year since 1950 except for 1987.
While the last fifteen years have not been a great period for pitching in general, it has been a surprisingly good period for a small handful of individual pitchers. The quartet of Roger Clemens, Randy Johnson, Greg Maddux and Pedro Martinez, was able to post extraordinary numbers during this period despite the increase in offense. Several other pitchers such as Zack Greinke in 2009, Mark Prior in 2003 and Kevin Brown in 1996 had one or more great seasons in this period as well.
In general, the last fifteen years, while tough for pitchers in general, has been something of a golden age for great pitching. Since 190, 108 pitches have posted an ERA+ of 175 or better in a season in which they pitched enough innings to qualify for the ERA title. While ERA+ is far from perfect measure of pitching dominance, it nicely and parsimoniously makes it possible to see a pitcher’s season in the context of the entire league. The 175 threshold, while somewhat arbitrary, is a good cutoff because it yield a number of pitchers, that is not too small for meaningful analysis, while not too inclusive. Of those 108 pitcher seasons, 26 have occurred since the resolution of the 1994 strike.
Almost a quarter of all of these dominant seasons occurred in the last fifteen years. This number is a little bit misleading because due to the switch to the five man pitching rotation and the current number of teams, there are now 150 spots in major league pitching rotations today, whereas there were only 64 (16 teams times four starters) for the first six decades of the last century.
Taking the switch to the five man rotation, which for the purpose of this calculation was dated, not entirely accurately to 1977, as well as the various waves of expansion, there have been 9,790 possible full time starting pitcher seasons since 1901 of which 2,250, or 22.9%, have occurred in the period from 1995-2009. In this context the 26 historic pitcher seasons, or 24% of the overall total, do not look as significant, suggesting there has not been a spate of dominant pitching seasons in the last fifteen years.
Most of the dominant pitching seasons of the 20th century, however, came during the deadball era as fully 34 of these 108 seasons came between 1901-1919. If we eliminate the deadball period from the sample and only include the years from 1920 to the present, the last fifteen years look somewhat different. During this period, 35% of the dominant pitching seasons have occurred since 1995, but these years only constituted 26% of the overall pitching seasons.
There are several possible explanations for this seemingly counterintuitive phenomenon. The first is methodological, as the league’s ERA increases, as it did during the last fifteen years, it is easier for pitchers to post ERAs that are significantly better than the league ERA. If the league ERA is 3.77, like it was in the AL 1958, it is a lot more difficult to be 75% better, even for the best pitchers, than when the league ERA is around 4.50 as it has been in the AL in most recent years.
This is, however, only a partial explanation, which is not entirely sufficient. It is possible that the emergence of Clemens, Johnson, Maddux and Martinez at around the same time is just something of a coincidence, a random event that has had a major impact on the game’s history, but there are other explanations as well One of the most significant is that better training, medical breakthroughs and, in the case of Clemens and perhaps others, steroids, allows great pitchers to keep pitching. Seventeen out of the forty seven seasons on the list in which the pitcher was over 30, six of the 14 seasons on the list in which the pitcher was over 35, and two of the three seasons in which the pitcher was over forty, have occurred since 1995.
Regardless of the reason, pitching seasons have not, in recent years continued the trend of regressing to the mean.,which they did for most of the middle of half of the period from 1920-1993. In fact, the reverse has occurred. Baseball fans have reaped the benefit of this because even during this period when the game’s balance has tipped to offense, we have been able to still see some fantastic pitchers. It is not clear whether or not this will continue, but Zack Greinke and Tim Lincecum, the two reigning Cy Young Award winners, whose ERA+ both exceeded 175 in 2009, are among those pitchers poised to continue this phenomenon into the next decade.