A discussion on the SABR mailing list regarding starters in the hall-of-fame, and the lack of starters born 1948-1961, led Stew Thornly to ask "When was the transition from three to four day' rest?". To start looking at this, I went to the Retrosheet game logs and looked at how many day of rest pitchers had. I ignored the first start of the year, and the first start after the 1981 strike. First, here is a graph showing the average number of says of rest. Since the average is skewed by spot starts of more than 50 day, I also plotted the average when limiting the starts to those with 10 or fewer day of rest.
Then I looked at the fraction of starts with each number of day of rest. Thus, in 2007 there were 4560 counted starts. 2515 of these were on 5 day rest, a rate of approximately 552 per thousand starts, 552&permil.
Starts on consecutive days peaked in 1879 at 367&permil.
Starts on 1 day of rest peaked in 1876, the first year of the NL, and had a lower peak in 1885.
Starting on 2 days of rest peaked in 1892 and rapidly declined when the mound moved back to 60'6", with a slight jump in 1901.
Starting on 3 days of rest peaked in 1897, 1920, and had it's largest peak in 1973, followed by a rapid decline.
Starts on 4 days rest have risen almost steadily, peaking in 1995 at 620&permil, and have dropped in the last decade.
The frequency of starts with 5 days rest began rising rapidly in the 1970s, and jumped to a new level in 1998.
Starts with 6 days rest, peaked in 1942, when Ted Lyons was ending several successful years as a Sunday starter.
Here's a table of the fractional values for each season. DH means that the pitcher made a second start on the same day. 0day means that the pitcher made starts on consecutive days.
Year Avg DH 0day 1day 2day 3day 4day 5day 6day 7day 8day 9day 10day 1871 5.63 .000 .121 .183 .150 .108 .067 .054 .067 .033 .046 .021 .033 1872 5.64 .000 .193 .242 .138 .092 .084 .037 .046 .023 .020 .009 .023 1873 4.09 .003 .273 .225 .144 .083 .067 .016 .070 .027 .011 .005 .019 1874 3.47 .004 .309 .282 .160 .078 .038 .029 .033 .011 .000 .013 .000 1875 4.65 .000 .296 .290 .120 .064 .064 .030 .027 .017 .009 .006 .008 1876 3.59 .002 .201 .412 .197 .044 .042 .010 .006 .008 .002 .018 .010 1877 3.65 .000 .333 .281 .123 .088 .041 .020 .029 .015 .009 .012 .009 1878 3.93 .003 .263 .340 .134 .080 .034 .023 .034 .006 .011 .009 .009 1879 3.16 .003 .367 .294 .141 .070 .024 .024 .016 .003 .006 .003 .008 1880 3.33 .006 .316 .263 .151 .090 .066 .021 .015 .014 .009 .011 .003 1881 3.93 .002 .189 .230 .199 .124 .079 .056 .047 .005 .012 .008 .011 1882 4.28 .004 .140 .248 .210 .134 .079 .048 .038 .022 .022 .009 .006 1883 3.81 .001 .158 .268 .235 .124 .078 .041 .022 .017 .009 .009 .005 1884 4.26 .001 .093 .295 .250 .138 .070 .038 .031 .013 .011 .012 .008 1885 4.30 .003 .040 .309 .254 .148 .087 .045 .030 .016 .014 .008 .005 1886 4.56 .002 .039 .278 .278 .157 .094 .042 .022 .016 .011 .008 .006 1887 5.04 .003 .027 .209 .265 .199 .092 .056 .039 .026 .015 .010 .004 1888 5.18 .001 .021 .191 .261 .195 .112 .065 .037 .022 .016 .015 .011 1889 5.10 .002 .022 .219 .238 .178 .099 .071 .048 .021 .021 .014 .009 1890 5.08 .005 .030 .194 .260 .178 .106 .059 .046 .022 .019 .012 .011 1891 4.84 .004 .028 .164 .285 .200 .111 .065 .040 .017 .015 .010 .008 1892 4.89 .005 .022 .178 .295 .219 .102 .055 .040 .017 .009 .009 .006 1893 5.14 .003 .015 .120 .281 .237 .117 .065 .049 .023 .020 .009 .007 1894 5.46 .003 .015 .107 .258 .234 .149 .059 .046 .027 .019 .013 .011 1895 5.65 .001 .014 .112 .243 .208 .136 .073 .063 .032 .023 .011 .011 1896 5.99 .000 .007 .091 .234 .215 .150 .087 .064 .035 .022 .013 .009 1897 5.77 .003 .013 .047 .210 .308 .147 .066 .057 .032 .021 .017 .014 1898 5.94 .002 .011 .048 .176 .265 .180 .103 .055 .033 .028 .021 .013 1899 6.00 .001 .008 .035 .184 .263 .178 .114 .061 .032 .027 .020 .012 1900 6.62 .000 .010 .031 .124 .225 .188 .135 .084 .051 .034 .028 .012 1901 5.60 .001 .008 .058 .212 .253 .161 .110 .063 .032 .022 .018 .013 1902 5.86 .000 .010 .048 .186 .243 .169 .113 .072 .037 .024 .024 .014 1903 6.19 .003 .006 .046 .160 .241 .189 .118 .066 .043 .026 .019 .014 1904 6.08 .002 .005 .039 .162 .276 .209 .095 .064 .033 .021 .015 .015 1905 6.46 .002 .007 .031 .156 .246 .196 .112 .069 .036 .026 .019 .019 1906 6.38 .001 .008 .031 .124 .246 .224 .116 .065 .043 .025 .021 .015 1907 6.93 .002 .010 .026 .123 .220 .200 .115 .080 .043 .035 .028 .015 1908 6.63 .003 .011 .042 .137 .230 .175 .119 .077 .036 .035 .021 .015 1909 7.63 .001 .008 .042 .123 .205 .160 .121 .083 .057 .044 .021 .018 1910 7.47 .001 .006 .018 .113 .218 .199 .103 .079 .047 .049 .027 .023 1911 7.98 .000 .006 .020 .113 .197 .182 .114 .083 .061 .042 .027 .023 1912 7.26 .000 .007 .025 .106 .246 .187 .115 .077 .049 .036 .025 .019 1913 7.15 .000 .010 .025 .102 .243 .196 .123 .075 .045 .035 .023 .017 1914 7.03 .001 .008 .030 .123 .256 .181 .112 .078 .042 .035 .016 .017 1915 6.97 .002 .008 .028 .114 .238 .188 .112 .088 .046 .034 .024 .017 1916 7.10 .004 .004 .024 .133 .248 .165 .100 .076 .053 .037 .023 .021 1917 7.12 .004 .006 .022 .103 .250 .190 .116 .069 .053 .032 .030 .018 1918 6.07 .003 .009 .030 .137 .296 .203 .103 .058 .036 .022 .015 .015 1919 6.77 .001 .007 .021 .102 .301 .206 .103 .057 .043 .029 .018 .013 1920 6.50 .001 .004 .018 .090 .322 .211 .115 .057 .039 .027 .027 .013 1921 6.99 .002 .006 .017 .075 .316 .211 .107 .061 .039 .029 .019 .016 1922 6.92 .001 .004 .019 .081 .302 .208 .113 .067 .044 .029 .023 .019 1923 7.05 .001 .006 .017 .074 .314 .211 .103 .071 .045 .032 .017 .013 1924 7.18 .001 .003 .016 .061 .284 .230 .111 .065 .046 .030 .023 .016 1925 7.28 .000 .003 .010 .042 .257 .253 .144 .073 .051 .034 .022 .016 1926 7.23 .000 .003 .016 .045 .232 .270 .145 .073 .044 .034 .019 .016 1927 7.31 .000 .003 .012 .050 .233 .256 .155 .083 .047 .027 .023 .017 1928 7.37 .000 .003 .009 .042 .218 .265 .159 .090 .050 .028 .023 .015 1929 7.53 .000 .005 .013 .038 .258 .249 .136 .081 .046 .030 .023 .018 1930 7.11 .000 .002 .010 .042 .272 .256 .136 .078 .046 .033 .020 .014 1931 7.12 .000 .002 .010 .054 .248 .241 .141 .094 .048 .033 .018 .022 1932 7.31 .000 .005 .017 .059 .236 .235 .145 .087 .048 .029 .019 .016 1933 7.35 .000 .002 .014 .060 .212 .252 .145 .098 .057 .032 .022 .014 1934 7.22 .000 .004 .016 .054 .243 .249 .151 .095 .044 .023 .020 .014 1935 7.38 .000 .004 .014 .060 .240 .220 .143 .086 .048 .033 .027 .018 1936 7.13 .000 .003 .014 .066 .268 .233 .152 .074 .044 .025 .022 .013 1937 7.46 .001 .002 .014 .049 .257 .237 .142 .096 .046 .026 .021 .014 1938 7.63 .000 .002 .008 .056 .271 .227 .143 .083 .038 .032 .018 .014 1939 7.42 .000 .000 .010 .049 .240 .231 .151 .105 .045 .030 .024 .016 1940 7.32 .000 .001 .009 .037 .255 .234 .138 .115 .054 .035 .024 .012 1941 7.77 .000 .001 .008 .024 .235 .230 .167 .113 .053 .030 .017 .013 1942 7.82 .000 .001 .012 .025 .187 .236 .168 .143 .050 .037 .023 .018 1943 7.49 .000 .001 .008 .042 .244 .217 .152 .123 .049 .029 .016 .019 1944 6.90 .000 .001 .006 .053 .250 .240 .140 .114 .048 .038 .019 .013 1945 7.42 .000 .003 .011 .042 .256 .225 .128 .119 .056 .030 .020 .014 1946 8.15 .000 .000 .002 .025 .198 .249 .152 .114 .056 .039 .023 .018 1947 7.53 .000 .002 .003 .039 .246 .255 .146 .095 .054 .031 .018 .011 1948 7.35 .000 .000 .011 .036 .218 .269 .154 .094 .050 .032 .021 .017 1949 7.11 .000 .001 .009 .042 .207 .301 .162 .089 .039 .026 .025 .013 1950 7.39 .001 .002 .007 .038 .258 .273 .139 .093 .043 .025 .018 .014 1951 7.34 .000 .001 .005 .023 .221 .281 .165 .103 .044 .029 .020 .016 1952 7.36 .000 .002 .005 .028 .208 .287 .163 .099 .036 .029 .026 .018 1953 7.31 .000 .000 .007 .028 .205 .277 .173 .104 .042 .034 .024 .013 1954 7.45 .000 .001 .005 .025 .209 .320 .161 .094 .043 .023 .019 .010 1955 7.29 .000 .000 .005 .022 .204 .313 .152 .085 .051 .032 .023 .015 1956 7.31 .000 .000 .011 .030 .255 .300 .145 .079 .038 .020 .017 .014 1957 7.26 .000 .000 .007 .024 .237 .324 .143 .083 .037 .030 .017 .015 1958 7.10 .000 .002 .005 .018 .275 .304 .155 .075 .041 .024 .014 .008 1959 7.03 .000 .000 .005 .014 .285 .311 .134 .083 .037 .020 .010 .014 1960 6.88 .000 .000 .003 .021 .252 .329 .146 .081 .042 .022 .016 .015 1961 6.88 .000 .000 .003 .020 .244 .350 .163 .074 .027 .021 .016 .009 1962 6.87 .000 .000 .003 .018 .290 .334 .143 .068 .037 .013 .015 .012 1963 6.58 .000 .000 .003 .013 .323 .318 .138 .061 .029 .023 .017 .011 1964 6.68 .000 .000 .002 .016 .304 .337 .128 .063 .036 .020 .016 .011 1965 6.56 .000 .001 .005 .015 .350 .321 .119 .054 .026 .014 .013 .007 1966 6.49 .000 .000 .003 .017 .365 .291 .112 .061 .034 .025 .017 .010 1967 6.56 .000 .000 .004 .013 .303 .341 .147 .068 .025 .017 .013 .009 1968 6.28 .000 .000 .002 .011 .322 .365 .130 .048 .027 .018 .011 .011 1969 6.57 .000 .001 .002 .012 .348 .337 .118 .062 .021 .017 .011 .009 1970 6.45 .000 .000 .001 .011 .315 .385 .133 .045 .022 .015 .013 .008 1971 6.38 .000 .000 .000 .012 .285 .413 .128 .052 .023 .016 .013 .008 1972 6.40 .000 .000 .001 .023 .320 .348 .149 .051 .022 .017 .008 .007 1973 6.23 .000 .000 .002 .024 .370 .357 .105 .034 .024 .014 .007 .007 1974 6.23 .000 .000 .001 .006 .334 .386 .123 .042 .025 .013 .009 .008 1975 6.28 .000 .001 .001 .008 .328 .376 .121 .046 .029 .019 .010 .008 1976 6.37 .000 .000 .002 .007 .235 .441 .144 .051 .029 .014 .013 .008 1977 6.53 .000 .000 .001 .007 .243 .411 .163 .058 .024 .017 .014 .007 1978 6.60 .000 .000 .001 .005 .207 .433 .164 .064 .029 .019 .013 .010 1979 6.87 .000 .000 .001 .003 .180 .472 .169 .044 .026 .020 .016 .008 1980 6.64 .000 .000 .001 .003 .150 .502 .178 .052 .026 .012 .014 .008 1981 5.66 .000 .000 .000 .002 .160 .530 .190 .045 .017 .009 .011 .013 1982 6.66 .000 .000 .001 .004 .125 .521 .197 .045 .020 .014 .013 .008 1983 6.68 .000 .000 .000 .002 .109 .536 .202 .049 .019 .013 .012 .010 1984 6.73 .000 .000 .000 .002 .082 .561 .195 .049 .021 .015 .016 .007 1985 6.60 .000 .000 .000 .003 .114 .544 .186 .049 .023 .013 .014 .008 1986 6.48 .000 .000 .001 .003 .099 .551 .212 .040 .021 .013 .010 .009 1987 6.60 .000 .000 .001 .001 .074 .571 .207 .047 .021 .013 .016 .006 1988 6.49 .000 .000 .000 .002 .054 .571 .235 .042 .021 .016 .013 .007 1989 6.53 .000 .000 .000 .001 .061 .561 .237 .042 .018 .014 .014 .008 1990 6.70 .000 .000 .000 .004 .048 .612 .204 .041 .018 .013 .012 .006 1991 6.58 .000 .000 .000 .002 .034 .597 .235 .041 .016 .011 .014 .010 1992 6.83 .000 .000 .000 .001 .016 .599 .241 .044 .022 .015 .013 .008 1993 6.75 .000 .000 .000 .002 .030 .591 .240 .037 .021 .011 .015 .010 1994 6.25 .000 .000 .000 .001 .024 .595 .247 .041 .016 .015 .015 .010 1995 6.45 .000 .000 .001 .002 .050 .620 .204 .036 .016 .009 .011 .008 1996 6.75 .000 .000 .000 .001 .026 .598 .236 .043 .019 .014 .011 .006 1997 6.79 .000 .000 .000 .001 .023 .589 .237 .050 .020 .011 .012 .010 1998 6.51 .000 .000 .000 .001 .010 .569 .284 .056 .019 .012 .012 .005 1999 6.72 .000 .000 .000 .000 .015 .537 .310 .050 .014 .011 .011 .011 2000 6.84 .000 .000 .000 .001 .010 .553 .298 .042 .020 .011 .013 .006 2001 6.90 .000 .000 .000 .000 .007 .520 .314 .044 .023 .011 .014 .010 2002 6.84 .000 .000 .000 .000 .004 .564 .284 .054 .022 .015 .011 .007 2003 6.73 .000 .000 .000 .001 .011 .538 .304 .062 .016 .014 .010 .008 2004 6.80 .000 .000 .000 .001 .011 .540 .304 .051 .023 .014 .008 .008 2005 6.45 .000 .000 .000 .000 .009 .565 .305 .040 .018 .014 .010 .008 2006 6.91 .000 .000 .000 .000 .007 .548 .310 .043 .018 .013 .011 .009 2007 6.90 .000 .000 .000 .000 .005 .552 .303 .044 .018 .014 .011 .007And here's a nine-year moving average. To compute these averages, I took the mean of year-4 through year+4, the unweighted average of the fractions.
