The End of an Era? Not Exactly...

This idea for this post was formed when I asked Jeff what seemed to be a simple question:  where have all the strikeout pitchers gone?  We both agreed that there are some really good strikeout pitchers in the game today--Rich Harden, Tim Lincecum, Justin Verlander, Jonathan Sanchez and Jon Lester have been the top 5 this year, in that order in strikeouts per 9 innings pitched (min 140 innings pitched).  (Interestingly enough, the oldest of these pitchers is Rich Harden at 27 years old, so perhaps there is another era of great K performances in the not so distant future.)

But, the above notwithstanding, there was a stretch of time in the late 1990s and early 2000s that lent itself to the strikeout pitcher.

Take a look at this chart (click the picture for a larger view, but the general idea can be seen):

There is a clear spike in the number of pitcher games with more than 12 strikeouts beginning in 1997 and lasting through 2002.  Now, take a look at this:

This is the same chart, with a line inserted to show the average number of pitcher games over 12 Ks for the years 1990-1996+2003-2009, compared to the average from 1997-2002.  The lower of the two lines falls at 24 pitcher games per year with 12K+ performances.  From 1997 to 2002 it goes up to 46.5 games per year, almost double!  It was during this stretch that we saw two 20K and two 19K performances, one 18K game, six 17K games and thirty-five(!) 15-16K performances.  In total, there were 509 pitcher games of 11Ks or more during this 6 year stretch, or 85 a season. By comparison, in the years 1990-1996 and 2003-2009 (a 14 year period), there were 721 pitcher games of 11Ks or more, or 52 per season.

During this period, Al Leiter, Pedro Martinez, Ron Villone, Kerry Wood, Randy Johnson, Curt Schilling, Roger Clemens, David Cone, David Wells, Mike Mussina, and Sterling Hitchcock. All turned in at least one 15K performance.

So what's the explanation?

Jeff suggested that perhaps batters' approaches to hitting have changed as we have migrated away from the so-called steroid era to a more contact oriented approach.  So I took a look at the stats, and it really doesn't support that theory.  Batters are striking out at a higher per game rate than any other time in history in 2008 and 2009.  And pitching K/9 is actually the highest in history as well.  If anything, the statistics suggest that we should be seeing pitchers posting better strikeout totals (although some of the K inflation may have to do with the introduction and widespread use of power relievers earlier in games).

So, if it's not the general K rate across baseball, there must be another explanation, right?  Well, in short, yes.

Of the top 10 K/9 full season performances in pitching history, 9 of them occurred during the time period '97-'02, and 14 of the top 20.  Pedro Martinez and Randy Johnson had 8 of those 9 (Kerry Wood had the other) and became the only two starting pitchers in the history of the game to post a  K/9 ratio over an entire season that topped 13 K/9 in 1999 and 2001, respectively.  From 1995 to 2001, the Big Unit put together seven consecutive seasons with a K/9 ratio over 12 (for some historical perspective, the all-time K leader Nolan Ryan had exactly 0 such seasons in his career).  In a fascinating example of absolute dominance, Pedro and RJ together accounted for 29 of the 46 games of 15Ks or more from 1997-2002.

Bottom line, during that time period two of the most prolific strikeout pitchers pitched through the prime of their careers (in terms of performance).  I put up the graphs above showing the number of pitcher games of 12+ Ks each season since 1990.  During the 6 year spike, there were 279 such games.  100 of them were accounted for by Pedro Martinez or Randy Johnson.  I'm going to repeat that.  100 out of the 279 pitcher games with 12 or more Ks were turned in by Pedro or RJ.  Let that sink in for a second because it is beyond phenomenal; they represented almost 36% of all 12K+ performances during the time period.  If you cut them out of the data, the average 12K+ performances per season drops from 46.5 to 29.8, much closer to the other years.

I also mentioned earlier that there were 509 pitcher games of over 11Ks from '97-'02.  Of those, 149 of them were turned in by either Pedro or RJ.  If you cut out those 149, the average per season drops from 85 all the way to 60, which would only represent an 8 game jump per season over the other years pointed out (still a jump, but could be partly explained by other future HOFers Curt Schilling, Roger Clemens and Mike Mussina, along with a couple effective seasons by power pitchers such as Mark Prior and Kerry Wood during this time).

In sum, the K spike was due in majority part to the dominance of two players.  Since then, we've seen the decline of two phenomenal careers (both pitchers are still effective today, but not nearly as prolific in terms of Ks).  RJ and Pedro turned in the single two seasons in all of MLB history averaging over 13K/9; they put in 149 games of 11Ks or more and 100 games of 12Ks or more (the majority of these being the Big Units).  So have we seen the end of an era?  Perhaps, but to be called an era I think the spike would need to be far more widespread.  In this case, we really just had the opportunity to witness two future HOF pitchers put together an amazing 6 year stretch of concurrent strikeout dominance.  Not only that, but they are the two best pitchers in the history of the game in terms of K/9, the only two career starters to post a K/9 of greater than 10, both better than Nolan Ryan. (This excludes Kerry Wood, who now pitches as a reliever which helps to keep his ratio high).

In this type of historical context, it becomes clear that it wasn't an era of strikeout pitchers, it was just the two greatest strikeout pitchers of all time pitching at the same point in history.