zig-zag wanderin' friend the Buzzin' Fly...) to get on with what promises to be some really pro-vo-ca-tive material, but here's a fun little stopgap in the meantime.
This is the chart that shows the "days of rest" percentages for starting pitchers since that data became readily available from daily logs first compiled by our old friends at Retrosheet (no age-ism intended in that statement, by the way) and formatted more felicitously for visual presentation by our somewhat younger old friends at Forman et fil.
As you can see, rest patterns for starters have shifted more than dramatically over the past thirty-five years, as the lines for short rest (SDR%, 3 days or less), long rest (LDR%, 5 days or more), and four days of rest (4DR%) demonstrate. Short rest was always at or near the greatest preponderance of the usage options adopted by managers until 1975, when a descent began that is nothing more or less than asymptotic.
The advent of the five-man starting rotation in the 70s reached its peak in the mid-1990s, but began to decline in the last decade, and in 2011--for the first time--was eclipsed as the predominant usage pattern by long days of rest. Will that pattern continue? Is that somehow related to the resurgence of pitching in the last several years? This is not the time for any glib answers or hasty conclusions. We will keep an eye on it, so stay tuned.
The fourth line, at the top of the chart, tracks the percentage of innings that starting pitchers contribute over the course of an individual season. A slow but steady decline from three-fourths of the total innings to under two-thirds occurred over sixty years; that, too, has shown a small reversal over the past couple of years.