To look at MLB’s history of leaguewide statistics is to see a catalog of its rule changes. In an otherwise gently undulating landscape of trends, the changes cause the spikes and bounces and dives. It’s not hard to look at a graph of league ERA and figure out that the mound was lowered in 1969, for instance, or to examine average slugging percentages and guess that something like the designated hitter came along in ‘73.
Or to look at stolen base numbers and see that something clearly seismic is happening in 2023.
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