PROOF OF POOF! THE SEPTEMBER FATIGUE FACTOR QUANTIFIED

Come to think of it,
Otsego Lake (adjacent to
Cooperstown) does look a
whole lot like a footprint...

Let's face it, folks, there are precious
few sabermetric discoveries that are
anywhere near as earth-shaking as
this footprint...

We don't want to oversell this discovery--heaven forfend that we follow in such large, loamy footprints with enough water in the mushy tread to fill Ostego Lake several times over.

This is just one of those essays that comes under the heading of "unfinished business," dating back to a discussion that we had with one of the more engaging contributors to BBBA, expatriate math professor Gerry Myerson, who since bidding us adieu (with a twirl of his moustache...) has been moonlighting as a folksinger and has been spotted as a headliner at a Sydney clogspot called The Loaded Dog.

Gerry had expressed extreme skepticism (in his case, that would amount to a slightly raised eyebrow...) about a claim we made that there was a pervasive tendency for September baseball to have lower offensive levels. (We'd eyeballed some data from one of the primordial sources available to us in the 90s, and had extrapolated from it that there was a 7-8% drop in offense in the final month of the season.

Several thousand fortnights later, we can now report that both of us were right. Thanks to the new "splits" tool in the Play Index at Forman et fil, we can compare components of offensive performance to the league averages and lasso them into charts and graphs. That means we can isolate months' worth of data, in this case data summed up to MLB levels, and compare them with the overall performance levels for each year.

When we do that (in the chart above left), we find that, for the years 1916 to 2012, overall offensive levels (as measured by OPS) are down in September-October by .013, or about 4%. We've chosen to show the data in running five-year averages, and that chart shows us that the downward trend, while pervasive, definitely appears to be weakening in recent times.

Rather interesting to note that hitters started taking a September swoon right at the beginning of the Depression (feel free to page Dr. Freud...but last we heard he was opening for Gerry at The Loaded Dog). Out of 95 years worth of data, there have been only eleven Septembers when the hitters have hit higher during that month than for the year as a whole. Three of those eleven, however, are in the last decade (2007, 2008, and 2011). In the last thirty years, the decline has--well, declined--to just -.007, less than half the gap from 1916-79 (-.016).

The reasons for such a pattern have to be somehow related to fatigue; cooling temperatures might be part of it, too. (We might find that the eleven years where the OPS was higher than average resulted from hotter than average Septembers.)

So, yes, Gerry, there is a downward trend in September; but it wasn't quite as big as we thought it was. (Though it used to be bigger. Come to think of it, many things used to be bigger...but that's another story for another time--and probably another continent.) Keep on s(w)inging, Gerry...