quote:

ORIGINAL: KG Erwin

Here's a stat that is commonly misunderstood. First of all, you gotta understand what an earned run is.

From wikipedia:

"In baseball, an earned run is any run for which the pitcher is held accountable (i.e. the run did not score as a result of a fielding error or a passed ball). If a run is not earned, it is an unearned run. Even if a runner scores on a fielding error by the pitcher himself, it is an unearned run.

Earned runs are specially denoted because of their use in calculating a pitcher's earned run average.

In determining earned runs, the official scorer must reconstruct the inning as it would have occurred without the errors (which include catcher's interference) and passed balls, with the benefit of the doubt always being given to the pitcher in determining which bases would have been reached by errorless play.

A run is counted as unearned when:

The baserunner would have been out had an error not been committed.
The run is scored after an error is committed that would have made the third out
A baserunner scores on a play where an error was committed, and the inning ends before that runner would have had a chance to score. Example: A passed ball allows a runner to score. The batter at the plate then strikes out to end the inning. The run is unearned. If the batter had instead got a base hit, the run would be earned, since the runner would have scored on that play.
In most other cases, a run is scored as an earned run."

Now, to calculate earned run average, here's the formula:

(Number of Earned Runs x 9) divided by (Number of Innings Pitched)

Generally speaking, this is an indicator on how effective your pitchers are.