Complex sentence: On September 23,2001, the Cup Series returned to racing at Dover after the September 11 attacks for the MBNA Cal Ripken, Jr.400, in which Dale Earnhardt Jr. received the checkered and American flag at the same time.
Split into simpler sentences: On September 23,2001, NASCAR Sprint Cup Series returned to racing at Dover after the September 11th attacks. In which Dale Earnhardt Jr. received the Checkered and American flag at the same time.