Differences Between SP And RP Since 1950

Beyond the Box Score's very own Glenn DuPaul wrote a terrific article yesterday on the correlation between RA9-Wins and pitcher's rWAR, which led to a fascinating discussion over at The Book Blog about replacement-level and the stark differences that exist between starting pitching and relief pitching. To help illustrate these differences, I've compiled a quick look at retrosheet's account of various metrics for both SP and RP since 1950.

The full spreadsheet can be viewed HERE, if you're into that kind of thing. For the short and sweet account, however, I've put together a (sortable) table of the percent change between the two roles after the jump.

For example, in 2011 RP strikeout rates were 16% higher than their SP contemporaries ( 20.6 RP K/PA / 17.7 SP K/PA = 1.16), while HR-rate was 15.4% lower (2.2 RP HR/PA / 2.6 SP HR/PA = .846).

Year BABIP K% BB% HR% ERA RA/9 wOBAA
1950 1.80 -2.97 20.43 -4.55 8.22 8.54 3.26
1951 -1.45 5.15 13.64 -5.00 0.73 2.40 -0.30
1952 0.00 2.73 9.52 0.00 0.00 3.10 0.00
1953 3.60 -0.93 10.84 -13.04 5.30 4.50 1.82
1954 2.20 5.66 9.52 -4.76 6.19 5.24 1.53
1955 0.00 -0.88 5.75 -12.50 -2.72 0.00 -1.22
1956 1.47 -2.46 10.59 -8.00 -2.23 0.44 1.24
1957 1.82 4.84 9.21 -12.50 -0.26 0.93 -0.63
1958 1.82 4.65 5.13 -16.00 -2.81 0.00 -1.56
1959 4.76 11.63 13.16 0.00 0.76 2.03 3.17
1960 0.00 8.33 10.26 -8.70 -4.35 -3.17 -1.25
1961 0.36 7.46 11.11 -11.54 -4.14 -2.37 -0.93
1962 0.36 7.97 14.10 -12.00 -5.17 -2.84 -1.86
1963 2.21 9.33 13.24 -13.04 0.29 2.27 -0.99
1964 1.44 11.26 8.82 -8.70 -5.71 -3.14 -1.63
1965 2.21 8.50 7.04 -17.39 -6.67 -3.69 -1.64
1966 1.82 2.61 2.99 -8.70 -3.34 -0.99 -0.33
1967 0.73 -0.63 0.00 -15.00 -3.25 -0.26 -1.01
1968 0.00 -3.13 4.62 -11.76 1.67 2.62 -0.34
1969 1.09 0.00 3.75 -4.76 1.93 1.70 0.64
1970 1.79 4.73 6.17 -12.50 -3.03 -1.13 -0.63
1971 0.36 6.38 10.81 -10.00 -2.27 -1.76 -0.97
1972 2.59 5.48 16.90 -15.79 -0.91 1.62 0.66
1973 2.51 7.46 7.79 -13.64 -1.58 -1.40 -0.31
1974 0.36 3.08 1.28 -5.56 -4.05 -2.84 -0.63
1975 1.42 4.69 5.00 -15.79 -9.09 -5.52 -1.56
1976 0.00 8.87 5.33 -12.50 -3.60 -3.66 -1.27
1977 -1.74 9.92 3.95 -8.70 -9.81 -8.33 -3.36
1978 2.88 12.30 9.33 -10.53 -2.92 -0.71 -0.32
1979 3.18 15.00 9.46 -17.39 -5.58 -3.90 -0.93
1980 0.00 15.00 5.56 -15.00 -10.95 -8.95 -3.42
1981 0.72 9.02 5.41 -16.67 -7.57 -7.02 -1.59
1982 -1.40 17.60 0.00 -18.18 -15.57 -13.60 -5.88
1983 -0.35 12.21 1.33 -18.18 -10.89 -9.29 -4.04
1984 -1.39 12.59 1.33 -9.52 -12.47 -11.14 -4.05
1985 0.00 11.85 1.28 -8.70 -5.99 -4.47 -3.13
1986 2.11 8.00 5.06 -16.00 -7.06 -6.11 -1.56
1987 1.39 13.42 2.50 -13.79 -8.30 -7.09 -3.35
1988 1.79 11.97 5.56 -14.29 -7.77 -5.84 -1.29
1989 -0.70 19.42 2.67 -15.00 -11.28 -9.89 -4.73
1990 0.35 12.59 2.60 -9.52 -9.45 -7.19 -2.50
1991 -0.35 14.48 2.53 -4.76 -8.13 -6.94 -3.13
1992 0.00 15.00 8.00 -15.00 -9.21 -8.60 -2.83
1993 1.37 19.01 7.89 -8.33 -5.79 -3.57 -1.83
1994 1.68 11.11 8.86 -7.41 -3.25 -1.98 -1.20
1995 0.34 15.58 11.11 -7.41 -5.03 -5.77 -1.80
1996 -0.99 17.20 15.19 -10.34 -8.37 -7.44 -2.96
1997 2.34 12.80 10.00 -7.41 -5.10 -4.06 -1.20
1998 -1.99 11.59 11.39 -14.29 -7.86 -7.41 -3.59
1999 -0.66 16.03 11.76 -10.00 -7.39 -6.40 -2.62
2000 0.00 13.29 11.63 -12.90 -6.52 -5.07 -2.62
2001 -2.35 17.07 8.00 -10.00 -9.59 -8.78 -4.53
2002 -1.02 15.63 9.09 -10.71 -9.19 -8.04 -3.94
2003 -0.68 16.03 10.67 -10.34 -8.57 -7.71 -3.63
2004 0.00 17.61 7.79 -10.00 -10.09 -8.91 -3.89
2005 0.00 16.03 15.49 -10.71 -5.91 -4.42 -2.45
2006 -0.99 16.98 10.81 -13.33 -10.59 -9.59 -4.18
2007 -2.30 17.39 12.00 -17.86 -9.87 -8.57 -5.06
2008 -1.33 16.27 12.99 -11.11 -8.48 -7.63 -3.92
2009 -1.66 13.37 13.92 -14.29 -8.91 -7.05 -3.92
2010 0.68 14.69 13.33 -11.54 -5.74 -5.51 -2.48
2011 -1.69 16.38 18.57 -15.38 -9.25 -9.13 -4.39

You'll notice that as the practice of match-ups based on handedness and shorter relief outings have become more popular in the past decade or so, the performance gap has grown dramatically. Strikeout rates have climbed and HR rates have fallen, leading to a steady 8% or so advantage in run-prevention for relievers over the past decade.

Note: all data includes post-season, wOBA does not include SB/CS, and weights taken from Fangraphs' "Guts!".

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