In 2020, we are seeing MLB 7-inning games in double-headers. Does this affect how the ERAs are calculated? MLB ERAs are normally calculated based on 9-inning games and High School ERAs are normally calculated based on 7-inning games which give different results. In a season with some 9-inning games and some 7-inning games, are two separate formulas used and then somehow combined? I know 7-inning games in DHs have been around in the minors for a while so I imagine this is well understood in some quarters but it is new to the MLB.

I’ve often wondered why ERA is figured based on 1 game (9 or 7 or whatever innings) versus 1 inning. I could understand if it were a stat that, taken to 3 decimal places, didn’t give very much information…like a stat that always came out like .001, .002, or even .0004 which would be rounded down to .000. But ERA is fine…3.75 per 9 innings comes out as .417 per inning…what’s wrong with that? Just like batting average, on base, slugging, etc. Games of different lengths aren’t combined in any sense, it’s just an average….all your ER divided by all your innings times 9.

Still, I don’t know how many people are aware that a high school ERA isn’t the same as a professional ERA, since it’s based on 7 innings, not 9. So if you gave up as many earned runs as innings pitched, in high school it would be 7.00, while in the pros it would be 9.00.

If anyone understands ERA, and is vested in whatever league they are in, will usually know the number of innings a game is. Therefor the ERA, looking at the letters, is E-arned R-uns A-verage. So it just gives an idea, that if a pitcher were to pitch a complete game, (7 or 9 innings… or whatever the league you’re in) how many runs they would give up. It helps to give managers an idea of how much a team needs to score to overcome the deficit their pitcher will put them in on average.

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