Why So Many No-Hitters?

I read a really interesting column in Sports Illustrated, full of anecdotal accounts from players, managers and well-informed baseball observers, explaining the perceived dramatic uptick in no-hitters so far this season.   With four no-hitters in a short period of time in the 2010 season, the most popular explanation has been steroids.  That was SI’s answer (see also here, here).  I’ve always been a bit puzzled by the steroid explanation because casual empiricism suggested that pitchers were benefiting from steroids too.  And less casual empiricism from Justin Wolfers — who took on the case of Roger Clemens — suggested the same thing (see also here).  Of course, its perfectly plausible that steroids benefit hitters more than pitchers  (but see here).  And the MLB home-run rate is low.  Also, there could be other explanations for an increase in no-hitters and/or perfect games, e.g. better defense.

Anyway, none of this is an attempt to provide a definitive answer.  Or even a not-so-definitive one.  The column just got me wondering about what the data look like.  I thought I’d show a picture that I put together based on the data from this CNN/SI column on the top 16 seasons for no-hitter frequency after 1901 to put things in context.

These data certainly are not conclusive.  But they seem to suggest that while 2010 is a good year for pitchers, and for no-hitters (the third highest no-hitter frequency at .18% thus far this season; the two best no-hitter seasons were 1908 and 1917 at .24%), the data also suggest that 2010 is not that unique.  Ten seasons since 1901 have had no-hit frequencies ranging from .15% to .18%.  Notice also that there are several high no-hit seasons from before the steroid era.  One explanation that is frequently tossed around is the increasing strike-out rate.  See below (the red line on top is strikeouts/9 innings):

No answers here.  Like most empirical questions, it is difficult to disentangle the determinants of the increasing strikeout rate.  But it strikes me that this trend at least as components that are entirely unrelated to the steroid era changes, e.g. changes in strategy or reduced stigma associated with striking out as it becomes an acceptable cost of hitting more home runs.  I’m no baseball expert.  But there seems to be some interesting stuff here.  Why has the strikeout rate increased so consistently over time?   How big of a deal was the steroid era anyway, in terms of relative performance of pitchers and hitters?

Discuss.