Complex sentence: The 2017 season is the Portland Thorns FC's fifth season of existence and plays in the National Women's Soccer League (NWSL), the top division of women's soccer in the United States.
Split into simpler sentences: The 2017 season is the Portland Thorns FC's fifth season of existence. The team plays in the National Women's Soccer League (NWSL), the top division of women's soccer in the United States.