Understanding Unearned Runs in Baseball: A Detailed Explanation

Question
Lead off runner gets on via an error.  Next two batters take walks to load the bases.  4th hitter hits a come backer to the pitcher to retire the lead off man at home.  Now, with one out and the bases still loaded, the pitcher walks the next batter allowing the run to score.  Is this run earned?

Answer
Konrad,

In this situation it will be considered an unearned run. While the pitcher retired the actual first batter when he got the force out at home, he should not have been on base anyway.

The only way a runner can be completely erased as an unearned run is if he was thrown out trying to steal second after reaching on the error. The runner being on third forces the pitcher to throw home, when he could have thrown to third or second had the original runner been put out.

Sean