REUTERS Sept 15 - Tennys Sandgren was defaulted from a tournament on Tuesday when the American accidentally struck a line judge with a ball after himself being hit in the groin. Sandgren, ranked 103rd in the world and top seed at the ATP Challenger event in Cary, North Carolina, doubled over after being struck by a ball bounced to him by a ball boy as he prepared to serve in the second game of the match against Christopher Eubanks. Sandgren then swiped his