Sunday, December 3, 2017

Annual AL Hitting In Innings 7-9 Relative to Innings 1-6, 1930-2017

All data from the Baseball Reference Play Index. Perhaps this gives us some idea of the impact of relief pitching over time.

For each year I found the OPS, OBP and ISO for the entire league in innings 7-9 and divided that by the corresponding numbers for innings 1-6 (OPSRatio, OBPRatio, ISORatio). Time line charts for each are below. The slope of the trend line for each one is

OPS) -.001
OBP) -.0006
ISO) -.0018

So maybe the strongest downward trend is for ISO.

Then I divided the 88 year period into eleven 8 year periods (I know, that is arbitrary). The table below shows each ratio for each 8 year period and again, it seems like ISO is the one that has dropped off the most. For example, from 1930-37, ISO in innings 7-9 was 3.2% higher than in innings 1-6. But from 2010-2017, it was 11.7% lower.

Anyway, all three stats have generally been in relative decline in the late innings.

Period OPSRatio OBPRatio ISORatio
1930-1937 1.016 1.015 1.032
1938-1945 1.009 1.020 0.982
1946-1953 1.008 1.013 0.994
1954-1961 1.006 1.010 0.993
1962-1969 0.997 1.007 0.972
1970-1977 0.998 1.010 0.965
1978-1985 0.984 0.999 0.950
1986-1993 0.968 0.987 0.920
1994-2001 0.955 0.979 0.906
2002-2009 0.938 0.973 0.877
2010-2017 0.938 0.970 0.883

Here are the correlations between the % of batters faced by relievers and the late to early hitting ratios

OBPRatio) -.686
OPSRatio) -.771   
ISORatio) -.713

So, as the % of batter faced by relievers increases, the OPS in innings 7-9 relative to innings 1-6 falls. The relationship is strong since the correlation is -.771. Squaring that (the r-squared) gets about .59, meaning that 59% of the variation across years in OPSratio is explained by changes in the % of batters faced by relievers. The more that relievers appear, the poorer the hitters do in late innings.

Here are the timeline charts







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