Page "Earned run" Paragraph 11

In the first two cases above, " on an error " includes situations where the batter makes a clean hit ( or walks, is hit by pitch, reaches base on a fielder's choice in which no out is made, or reaches base on a wild pitch on a called or swinging third strike ), but should have been out earlier in his at bat on a foul fly ball which was dropped by a fielder for an error.

This also includes any run ( or any subsequent run ) that scores on plays that result in outs with one out or a double play with none out if an error has extended the inning.