What is an ERA in Baseball? (Detailed Explanation)

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Statistics have been a big part of sports ever since we began playing organized sports. From the most basic stats such as hits and strikeouts to the more complex ones like WAR and OPS, stats have and always will be the way we quantify teams and their players’ abilities.

When it comes to pitching, there are several ways to evaluate a pitcher’s effectiveness through stats. One of the most popular pitching stats is ERA.

ERA stands for earned run average. It is the average number of earned runs that a pitcher gives up each game over the course of a season. It is the most common statistical tool to evaluate a pitcher’s effectiveness.

Unlike most offensive stats, a pitcher’s goal is to keep his ERA as low as possible. The lower the ERA, the fewer earned runs he is likely to give up in a game.

ERA is fairly simple to understand, but there are some complexities to it that must be explained.

How is ERA Calculated?

ERA is calculated by using simple division and multiplication.

First, take the total earned runs given up and divide it by the total number of innings pitched. Then, multiply that number by nine, and there is your ERA. Here is a formula to follow:

(Total Earned Runs / Total Innings Pitched) 9 = ERA

Let’s look at an example of a player’s stat line for a game:

5 innings pitched, 3 runs, 2 earned runs, 5 hits, 7 strikeouts, 1 walk, 0 home runs

The only stats we need from this line to calculate his ERA are the innings pitched and the earned runs. Let’s plug those numbers into our equation and do the math:

(2 / 5) 9 = ERA

(.4) 9 = 3.6

The player’s ERA for that game is 3.6. Now, let’s look at a season stat line to configure the player’s ERA over the course of a season:

47 innings pitched, 23 runs, 15 earned runs, 56 hits, 48 strikeouts, 10 walks, 5 home runs

Still, all we need from this line is the innings pitched and earned runs.

(15 / 47) 9 = ERA

(.319) 9 = 2.87

His ERA over the course of the season would be 2.87. This tells us that if this player were to pitch an entire nine-inning game, based on his performance in the innings that he has pitched, these stats predict that he would give up 2.87 runs that game.

Obviously, it is impossible to give up a fraction of a run, but remember, this number is just an average.

Some people are often confused by the number nine. Remember, ERA is the average number of earned runs a player gives up over an entire game if he were to pitch every inning. Professional leagues play nine innings, so that is why the number nine is multiplier.

In leagues where games are only seven innings, it makes sense to multiply the number by seven because that is considered a complete game. Still, some high school and youth leagues use the number nine to configure a player’s ERA, but this should not be the case.

This is not fair to the pitcher who will never throw more than seven innings in a regulation game. Why should his ERA reflect two extra innings that he will never throw?

Let’s look at the difference this makes in calculating a player’s ERA. Here is the season stat line of a high school pitcher:

23 innings pitched, 18 runs, 11 earned runs, 17 hits, 31 strikeouts, 12 walks, 1 home run

Here is his ERA calculated using seven as the multiplier:

(11 / 23) 7 = ERA

(.478) 7 = 3.34

Now here is his ERA calculated using nine as the multiplier:

(11 / 23) 9 = ERA

(.478) 9 = 4.30

As one can see, this makes a big difference in the player’s ERA. High school teams and leagues should always adjust their ERA calculations if their games are shorter than the typical nine-inning game.

What is an Earned Run?

An earned run is any run that is scored by the offense that is at the fault of the pitcher. Here are some scenarios that will help better understand what is considered an earned run and what is not.

If a player hits a home run, the pitcher is charged with one earned run. The pitcher threw the pitch and gave up the run by no one’s fault but his own; therefore, he is charged with a home run.

If a pitcher walks a batter then gives up a hit, and then both of those players score later in the inning off of a double, then he is charged with two earned runs. He gave up the base runners who scored; therefore, they earned those runs off of the pitcher.

If a hitter reaches first on an error and then later scores on a hit that inning, the pitcher is not charged with an earned run. That player reached base at the fault of the defense, not the pitcher; therefore, the pitcher cannot be charged with the earned run.

In the previous scenario, it can be reasoned that the run only scored because the defense made an error. It is not fair to charge the pitcher with an earned run for something that he could not control. When calculating his ERA at the end of the game, the unearned run would not count.

The ERA is intended to be a reflection of the pitcher, not the defense. By distinguishing earned runs from unearned runs, the ERA is a more accurate depiction of the pitcher’s ability to keep opponents from scoring runs.

A run average that would encompass both earned and unearned runs would be more of a reflection of the defense as a whole and not just the pitcher. This is why only earned runs are counted into the pitcher’s ERA.

Is ERA a Reliable Statistic?

Baseball has recently become a numbers game in the eyes of many scouts and executives in the professional game. Many argue that a player’s worth can be quantified like never before using analytics.

These innovators in the world of baseball analytics have recently challenged the validity of some of the most basic stats that we see on our TVs and computers today.

For example, people in the analytics field of the sport view batting average as one of the more superfluous offensive stats. Instead, they believe stats like on-base percentage, slugging percentage, and OPS provide more reliable intel on a player’s value.

The same goes for ERA. Some evaluators believe that there are more effective ways to evaluate a pitcher. Two of those methods are FIP and WHIP.

What is FIP?

FIP stands for Fielding Independent Pitching. Essentially, it is a number that reflects a pitcher’s effectiveness while taking his defense out of the equation.

It is believed by some statisticians that while ERA only factors earned runs into the equation, it still unfairly puts them on the hook for earned runs scored off of weak contact and other defensive miscues that technically don’t go in the book as errors.

FIP is calculated using only strikeouts, unintentional walks, hit-by-pitches, and home runs. Hits that don’t go over the fence do not count in FIP because, remember, defense is taken out of the equation altogether.

Here is the formula for FIP. (Note: it is not for novice mathematicians):

((13 x HR) + (3 (BB + HBP)) – (2 x K)) / IP + FIP Constant = FIP

One can probably see while only some of the most advanced leagues consistently calculate FIP.

The FIP Constant is an important part of the equation. It takes the league average ERA and places it into the same equation above to essentially come up with an average FIP across the league. Here is how it is calculated:

Lg ERA – ((13 x Lg HR) + (3 (Lg BB + Lg HBP)) – (2 x Lg K)) / Lg IP) = FIP constant

According to fangraphs.com, the FIP constant in most years is around 3.10.

So let’s take the professional player’s season stat line from earlier:

47 innings pitched, 23 runs, 15 earned runs, 56 hits, 48 strikeouts, 10 walks, 5 home runs

Let’s use 3.10 as the constant to calculate his FIP for the season:

((13 x 5) + (3 (10 + 0)) – (2 x 48)) / 47 + 3.10 = FIP

((65) + (30) + (96)) /47 + 3.10 = FIP

(-1) / 47 + 3.10 = FIP

-0.02 + 3.10 = 3.07

His Fielding Independent Pitching for the season would be 3.07. His ERA was 2.87, so his FIP being slightly higher than his ERA isn’t a major cause for concern since it is still below the league constant.

When a pitcher’s FIP is significantly higher than his ERA, it raises some eyebrows among evaluators. This may indicate that the pitcher relies heavily on his defense to keep runs off the board.

Pitchers who have a high ERA and a much lower FIP are often considered unlucky. They may give up a lot of weak contact hits that result in runs.

Some in the analytics field would take this type of pitcher over a pitcher with a low ERA and high FIP because they believe that he can do more on his own where the latter relies too much on his defense.

What is WHIP?

WHIP stands for Walks plus Hits per Inning Pitched. Here is the formula to calculate WHIP:

(Walks + Hits) / Innings Pitched = WHIP

This is similar to On-Base Percentage as it shows how many base runners a pitcher gives up each inning. A pitcher’s goal is for his WHIP to be as low as possible. Typically, a WHIP around 1.00 is considered exceptional.

The reason some evaluators look at WHIP over more popular stats such as ERA, strikeouts, and hits is that they believe base runners are the most valuable asset in the game.

Runners can’t cross home plate without touching first, second, and third base. With this in mind, it is an offense’s goal to get players on the bases, and it is the pitcher’s goal to keep them off the bases.

The lower the WHIP the fewer base runners the pitcher allows each inning. Fewer base runners equals fewer opportunities for the offense to score runs.

We should not completely ignore a pitcher’s ERA because there is something to be said for a pitcher who consistently produces low ERAs.

With that being said there are some stat categories that are starting to gain more attention among scouts and executives who are charged with quantifying a player’s value.

What is a good ERA?

Most people consider an ERA between 3.00 and 4.00 to be a good ERA. An ERA below 3 is considered to be an excellent ERA. Like most statistics, the quality of the competition in the league must be factored into how good the ERA is. An ERA of 3.7 in the Major Leagues is a lot more impressive than the same ERA at the local Little League.

Who holds the record for the lowest ERA in a season?

In 1937, Eugene Bremer of the Cincinnati Tigers in the Negro Leagues held a 0.71 ERA over 50 ⅔ innings. This is the lowest ERA in all of professional baseball. Tim Keefe holds the National League record with a 0.86 ERA in 1880. Dutch Leonard is the American League record holder with a 0.96 ERA in 1914. He did this over a whopping 224 innings pitched.

How do seven-inning games in the MLB factor into ERA?

While it may seem unfair, seven-inning games, as are now played in MLB doubleheaders, are not calculated any differently than nine-inning games. This is because the ERA is supposed to predict the number of earned runs a pitcher will give up over a regulation game, which in the MLB is nine-innings.

When was ERA first introduced?

Statistician Henry Chadwick first introduced ERA in the late 1800s. At the time, wins and losses were really the only way to track a pitcher’s effectiveness. Chadwick believed that record did not tell the whole story of a pitcher’s value, so he created ERA.

Who had some great career ERAs?

Ed Walsh currently holds the record for the lowest career ERA with 1.816 over 14 seasons. Mariano Rivera has the lowest career ERA for a modern-day pitcher with a 2.29 ERA over 19 seasons as the Yankees closer. Clayton Kershaw has the lowest career ERA among active pitchers with a 2.49 ERA in 14 seasons.

Can you have a zero ERA?

Yes, it is possible to have an ERA of 0.00, but only if you don’t give up an earned run. This is fairly common over the course of a game, but it is very rare over the course of a full season. It is also possible to have a 0.00 ERA even if you have given up runs. As long as the runs are unearned, they do not count toward your ERA.

References

https://www.baseball-reference.com/leaders/earned_run_avg_season.shtml