Parsing the DH era

In my post Sunday on run totals throughout baseball history, I noted a common myth: that the adoption of the designated hitter rule in 1973 jump-started baseball’s offensive era. In truth, run totals didn’t peak until the mid-1990s. That’s been lost on a number of prominent writers who rationalize the inflated ERA totals of any pitcher from the 1970s or later. Just Google “Jack Morris DH era.”

One irksome thing to a baseball historian like me is that sportswriters often treat the so-called DH era as one continuous stretch. What people call the DH era is more like three eras:

1) 1973-92, where American League teams averaged 4.41 runs, while NL teams averaged 4.12. Historically, the AL average was 0.9 percent higher than the average of 4.37 runs from the league’s founding in 1901 through 1972. The increase may have seemed more dramatic at the time, as AL teams had flat-lined at 3.88 runs a game from 1963 through 1972, after the Baseball Rules Committee changed the strike zone.

2) 1994-2009, where AL teams averaged 4.99 runs, while NL teams averaged 4.65. Whatever the reason or reasons, some seismic shift occurred in baseball in the early ’90s, leading to the highest sustained scoring levels in the circuit since the 1930s.

3) The past five seasons, where AL teams have averaged 4.39 runs, while National League teams have averaged 4.14. The current AL scoring rate is slightly below the all-time league scoring average through nearly 114 seasons of 4.5 runs per game.

Has it been harder to pitch in the American League since the DH was the instituted? Almost certainly. Overall, run totals in the American League have been roughly 6.5 percent higher than they have been in the National League since 1973. In all the years before that both leagues were in existence, AL teams enjoyed just a two percent advantage in scoring. So there’s been some boost with the DH, which seems reasonable given that pitchers have been replaced in batting lineups with the likes of Edgar Martinez and David Ortiz.

That said, I think the important thing is not treating all pitchers from the DH era the same. Morris’s 3.90 ERA and Mike Mussina’s 3.68 ERA are two radically different numbers, for one. In the years Morris pitched, 1977 through 1994, American League teams averaged 4.5 runs per game. During Mussina’s career, 1991-2008, the AL average was 4.91 runs. Looked at another way, Morris’s ERA was 13.3 percent better than league average while Mussina’s was 25.1 percent better.

I noted something along these lines yesterday on Twitter and someone replied that Mussina is among the most underrated players all-time. I agree. With a better understanding of run totals from Mussina’s era, maybe this can change.

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