Earned Run Average

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.

Rule 9.21 e) has not been adjusted in the 2021 MLB rulebook, so the 9-inning standard is maintained regardless of 7-inning double-headers, nor should it change.

As an official scorer in AAA affiliate ball for 10 years, I can confirm that the 9-inning standard to calculate the ERA has been used in the minor leagues, even though double-headers have been 7 innings for as long as I can remember, so there’s no reason why MLB should adjust the calculation on account of double-headers.

So what kind of “adjustment” are we talking about? Suppose half a team’s games were played as doubleheaders. That means 81 games of 7 innings, 81 games of 9 innings. An average game would be 8 innings, so would ERA be ER per 8 innings? (OK, I know 81 doesn’t divide by 2, but you see my point.) Trouble is, that would only work if every team had games of the same average length.

Instead, you could figure ERA as ER per 9 innings, but count an ER given up during a 7 inning game as 7/9ths of an ER. Either way, it’s completely unnecessary. After all, there is no “adjustment” if a game lasts 10 or 12 or 20 innings…or if it is shortened to 6  or 8 innings. And if ERA were per inning instead of per 9 innings, we wouldn’t even be having this discussion.