Complex sentence: It is the 41st edition of the Legg Mason Tennis Classic, and is part of the ATP 500 Series of the 2009 ATP Tour, and was the third men's event on the 2009 US Open Series.
Split into simpler sentences: It is the 41st edition of the event known that year as Legg Mason Tennis Classic, and is part of the ATP World Tour 500 series of the 2009 ATP World Tour. The Legg Mason Tennis Classic is the third ATP stop of the 2009 US Open Series.