Short answers, pulled from the story.
Demetrius Clements established a professional football club in Rock Island, Illinois during 1907. The new team had no ties to any athletic club or social group and received no corporate backing.
Walter Flanigan joined the organization as a backup end player in 1912 before taking ownership of the team in 1915. He later served as assistant manager under Jack Roche for two seasons and represented the squad at the league founding meeting on the 17th of September 1920.
The Rock Island Independents hosted an official game on the 26th of September 1920 against the St. Paul Ideals by a score of 48 to 0. Three thousand one hundred spectators watched Arnie Wyman make his debut for the Islanders during this event which marked the first NFL game between member teams.
Dale Johnson moved the Rock Island Independents to the rival American Football League in 1926 making them the only NFL franchise to join a competing organization. The new league featured star Red Grange but paid less than the NFL did leading players to leave the team seeking higher salaries elsewhere.
Douglas Park hosted matches from 1907 until 1925 inside Rock Island, Illinois at the corner of 18th Avenue and 9th Street. The venue currently houses baseball fields, soccer pitches, and a playground area while hosting annual rivalry games like the Rocktown Showdown.