What Does ERA Mean in Baseball?

What Does ERA Mean in Baseball?

ERA, or Earned Run Average is one of the most important stats for determining a pitcher's performance. It was originally created during the 1900s to rate the effectiveness of relief pitchers, and has evolved to be a major measuring stick at all levels of baseball for pitchers. Today, it is one of most widely recognized statistics in the game.

Definition

The statistic ERA measures the average number of runs given up by a pitcher over the course of a nine-inning game. An earned run is runs allowed by the pitcher excluding runs resulting from errors, or mistakes made by other players in the field, or runs scored by runners caused by the previous pitcher. An ERA is based on the runs earned over nine innings.

Calculations

An ERA is calculated by adding up the earned runs and dividing the number by the number of innings pitched. That number is then multiplied by 9. For example, if a pitcher allowed 25 earned runs over 100 innings, you would divide 25 by 100 and then multiply by 9. The ERA would be 2.25. It is possible for a pitcher to have an infinite ERA if he is unable to retire a batter whilst giving up runs.

Interpretation

The lower the ERA, the better the pitcher is considered. During the early 1900s, some pitchers had ERAs under 2.00 due to the lack of hitting during that era. However, as the rules of the game have evolved over the years, an ERA under 4.00 is now considered somewhat effective, while an ERA under 2.00 is rare. An ERA above 6.00 usually is considered unacceptable. It is important to also consider sample size as it can be very easy for a pitcher to have a low ERA if he pitches a small portion of innings. Bob Gibson currently holds the record for best in-season ERA with a 1.19 ERA in 1968.

Misconceptions

Some experts don’t consider ERA to accurately reflect a pitcher’s ability, or his success on the field Although it accounts for the ability to get batters out and prevent runs, it leaves out a variety of external factors that may skew the results. For example, a pitcher with a below average defense will suffer from his defense being unable to get runners out. Another major external factor is where the pitcher plays his home games, as some ballparks are more friendly to opposing batters than others. Recently, stats like ERA+ or Defense Independent Pitching Stats (or DIPS) have attempted to solve this by removing defensive attributes and accounting for locations.