Confidence: I'm as sure as I can be.
Notes: There are several reasons why I think this is a Common Darter. By the 20th of August the Ruddy Darter should be fully mature and this image is of a mature male darter dragonfly. A Ruddy Darter male should be showing red frons (face) surrounded by a black border, this is absent in this specimen. The abdomen is not sufficiently waisted or clubbed at the end to be a Ruddy Darter. There is a hint of light leg stripes and pale anterhumeral stripes which are absent in the Ruddy Darter. Finally the yellow thoracic patches are characteristic of the Common Darter, although present in the Ruddy Darter they will be much browner. ID has been made more difficult by the under carriage shot.