Complex sentence: From 1913 until 1917, Hemingway attended Oak Park and River Forest High School where he took part in a number of sports, namely boxing, track and field, water polo, and football.
Split into simpler sentences: From 1913 until 1917, Hemingway attended Oak Park and River Forest High School. He took part in a number of sports--boxing, track and field, water polo, and football.