Seattle was finally awarded a Major League Soccer franchise in 2007 . The Sounders debuted in the MLS in 2009 , winning the U.S. Open Cup . Seattle first put itself forward as an MLS franchise at the league 's inception in 1994 and , after several attempts , in 2007 the city was awarded a team thanks to the combined efforts of high-profile backers . They have won three Lamar Hunt US Cups and one Supporters' Shield since their inception as an expansion team in 2009. The Sounders play at Qwest Field , and had an average attendance of 30,897 .
Seattle was finally awarded a Major League Soccer franchise in 2007 . The Sounders debuted in the MLS in 2009 , winning the U.S. Open Cup . They have won three Lamar Hunt US Cups and one Supporters' Shield since their inception as an expansion team in 2009. The Sounders play at Qwest Field , and had an average attendance of 30,897 .