This is information about the league Ren plays in at the start of the story.
It is the top league of High Schools in Japan with 9 teams.
I will list all of the teams, along with their best players;
Osaka Kōkō High, Best Player:Itoshi Sakamoto (Left Wing) (Chapters 1-5). Takashi Ren (Striker) (Chapters 5-12). Daichi Morita (Centre Attacking Midfielder) (Chapter 13+)
Tokyo Gakuen FC, Best Player:Yorunobu Kisaki (Striker) (Chapter 1+)
Kyoto International Academy, Best Player:Haruto Fujimura (Midfielder)
Fukuoka Seiryu High, Best Player:Riku Yamamoto (Centre Back)
Nagoya Yūzai Academy, Best Player:Shinji Kato (Centre Attacking Midfielder)
Sapporo Tatsu High, Best Player:Taito Okazaki (Right Wing)
Kobe High FC, Best Player:Hiroshi Nakajima (Goalkeeper)
Sendai High School, Best Player:Koji Takeda (Centre Midfielder)
Yokohama High Academy, Best Player:Taichi Tanaka (Striker)