What is ERA in Baseball?

ERA stands for earned run average, which is an unofficial Major League Baseball (MLB) statistic that measures a pitcher’s effectiveness at giving up runs, per nine innings, in a specific baseball game. 

Evaluating the performance of pitchers in baseball has often been the subject of much debate. Statisticians, umpires, and basically everyone associated with the mechanics of the sport have looked for methods and techniques to evaluate a pitcher’s performance.

ERA, along with other factors, has proved to be the best tool. But what is ERA and how does it represent a player’s performance? Let’s take a look.


What is ERA in Baseball?

In baseball, the role of the pitcher is pretty straightforward—to block and prevent the other team from scoring. A pitcher’s ability and effectiveness in doing so is recorded as his/her earned run average.

But what is the earned run average based on? ERA is derived from the average number of earned runs allowed for every nine innings pitched, or for every nine-inning game, the traditional duration of a standard game.

While it isn’t officially recognized by Major League Baseball statistics, it’s still the most widely used tool for analyzing pitching performance. 

To understand it better, let’s delve into what constitutes earned and unearned runs. 

Earned and Unearned Runs Explained

Earned run average can be misleading, especially if it’s based on a single factor: the pitcher’s effectiveness at blocking the other team from scoring. 

To ensure the pitcher’s earned run average does not suffer because of poor or average defense, he can be charged with two different types of runs: earned and unearned.

What Is an Earned Run?

In an earned run, the run is made possible by the offensive team and great defensive play. It isn’t enabled by errors (such as a passed ball or fielding error) from the teams.

What Is an Unearned Run? 

Runs that occur because of passed balls and defensive errors are regarded as unearned runs. This type of run is omitted from the pitcher’s ERA calculations.

How Did ERA Come About?

The ERA pitching statistic was born in the 1900s as the brainchild of Henry Chadwick, an English sports writer, historian, and statistician. 

ERA became the measure for pitching effectiveness when relief pitching rose in popularity. (Relief pitching refers to the practice of sending in another pitcher after the starting pitcher is removed.)

Before people started using ERA, a pitcher’s performance was evaluated based on the win-loss record. There was no other measure of its kind since players were generally expected to pitch a complete game.

While baseball encyclopedias often include the ERAs for Negro League games, the figures were derived retroactively. They were based on total runs since they had yet to distinguish between earned and unearned runs.

Influence of the Designated Hitter Rule on a Pitcher’s ERA

The introduction of the designated hitter (DH) rule to the American League (AL) in 1973 made maintaining a low ERA challenging. The DH rule stipulated the inclusion of a DH who would bat in place of the pitcher. 

This rule effectively means that pitchers spending most of their careers in the AL were at a disadvantage in terms of ERA rates.

It’s, therefore, no surprise that the National League Pitchers (NLP) had overall good ERA scores in comparison to their American League counterparts. In contrast to the AL, the National League didn’t have a DH on their team and the AL’s pitcher usually wasn’t a very good batter. 

To even the playing field, the DH rule is now only implemented when regular season interleague games take place in an AL baseball park. This measure has been in place since 1997.

How to Calculate ERA

Calculating ERA is done by dividing the number of innings pitched by the pitcher’s total number of earned runs, and then multiplying the quotient by nine. 

Here is the ERA calculation formula:

ERA = 9 x total number of earned runs allowed (ER) / total number of innings pitched (IP)

A lower ERA is generally considered better. 

What Factors Do You Need to Take Into Consideration When Calculating ERA?

If you want to avoid manually calculating your favorite player’s ERA, you can use an ERA calculation tool. An ERA calculator automatically takes into account innings pitched, earned runs, and game innings. 

It may also include out-pitched innings in its calculation. However, out-pitched innings are optional, so feel free to exclude it from your equation.

A player’s ERA is also affected if the pitcher exits the game while there are runners on base. The runs scored by the runners will be counted against the pitcher and will negatively impact the pitcher’s overall score.

What is Considered a Decent ERA?

The answer depends on several variables. Just like a batting average, a good ERA varies depending on which decade you’re looking at. 

Here’s a quick look at how a good ERA in baseball has changed over the years:

  • 1900s and 1910s: Known as the dead ball era, the period was characterized by low scores and not many home runs. Good ERA ratings were below 2.00 (with two earned runs allowed for every nine innings).
  • Late 1920s to 1930s: ERA ratings were below 4.00. Statistics were influenced by strongly favored hitters. 

The highest caliber pitchers could score an ERA as low as 3.00. Examples include Dazzy Vance and Lefty Grove who would consistently post a low ERA.

  • 1960s: ERA ratings were below 2.00.
  • 2019: ERA ratings under 4.00.

Exceptional ERA Records

Noteworthy ERA records are usually based on who has the

  • lowest ERA in a season;
  • highest ERA in a season; and
  • lowest career ERA of all time.

Lowest ERA in a Season

The lowest single season ERA is credited to Dutch Leonard of the Boston Red Sox who achieved a 0.96 ERA in 1914. He pitched 224.2 impressive innings with a win-loss totaling 19-5. 

Dutch’s performance was one of the defining moments in baseball’s modern era, which started in 1901.

During the live ball era that began in 1920, Hall of Famer Bob Gibson of the St. Louis Cardinals is the rightful record holder of the lowest ERA, with a 1.12 score. He set the record in 1968 and pitched over 300 innings.

The 21st-century record holder for having the lowest earned run average in a season goes to active pitcher Zack Greinke of the Los Angeles Dodgers, with a 1.66 earned run average in 2015.

Highest ERA in a Season

The highest ERA in a season is by Les Sweetland of the Philadelphia Phillies who had the worst earned run average ever recorded in MLB history. He had a high ERA of 7.71.

Lowest Career ERA of All Time (More Than 1,000 Innings Pitched)

With an ERA of 1.79, Ed Walsh has the lowest career record between 1904 and 1917. 

During the live ball era after 1920, Mariano Rivera earned a 2.21 ERA from 1995 to 2013.

When it comes to active pitchers, the lowest career record for earned run average is held by Clayton Kershaw of the Los Angeles Dodgers. He achieved a 2.44 ERA during the 2019 season.

Is ERA Reliable?

While a pitcher’s ERA is designed to analyze and determine the performance of specific pitchers, it isn’t the most reliable measure because it doesn’t completely gauge one’s entire athletic performance. 

Another downside is that it can be influenced by factors that are beyond the pitcher’s control. In a bid to isolate pitcher performance, modern baseball employs sabermetrics, a tool that relies on empirical evidence and statistics to predict future performance and arrive at winning strategies. 

When it comes to pitching, sabermetrics uses defense-independent pitching statistics, or DIPs, to assess baseball pitching effectiveness.

Can You Judge Relief Pitchers Solely Based on Their Earned Run Average (ERA)?

No, it wouldn’t be fair to gauge relief pitchers on ERA alone. Performance should be evaluated with ERA and one to two other methods of measurement. 

Evaluating relief pitchers exclusively on ERA can lead to a significantly skewed analysis since ERA only takes into account the runs scored by the batter who made it to base while batting against the pitcher.

A relief pitcher enters the field with the knowledge that he or she will be in the game for a relatively short while. Unlike starters, relief pitchers’ limited role gives them the advantage of directing all their energy into each pitch.

Since they’re on the field for a few innings only, and at times with just a few batters, they can keep their ERA scores low. This is in stark contrast to starting pitchers who have to conserve energy in case they’re called in to pitch seven or more innings.

Does Location Affect Players’ ERA?

Absolutely. The park where a pitcher’s team plays half its games can strongly influence earned run average.

If we were to identify a team that faces challenging playing conditions due to the location of the baseball park and the climate, it has to be the Colorado Rockies. Imagine what it must be like to practice, prepare, and play in hot and dry weather with hardly any rain. 

In response to the challenging conditions, the team is known to store their balls in humidors before pitching so they can throw effective breaking balls.

Wrapping Up

Whether you’re a fan, a coach, or a baseball player, evaluating pitchers with ERA is a handy statistical measure. When combined with one or two other methods, you’ll be better able to track a pitcher’s effectiveness on the mound.