Hi Chef!

Each team will be assigned with a Team League, to begin with, based on their Win Points. Based on the team's performance in Team Tournament, a Team will be either Promoted to a higher league, Demoted to a lower league, or continue in the same League as well. 

Teams that finish in the top 3 ranks in any of the Team Tournaments are promoted to the next higher league if there is a higher league available. That is the Chef Teams who have earned Gold, Silver, or Bronze trophies. 

Teams that finish in the bottom 3 ranks of the team tournaments are demoted to the next lower league unless there is no lower league available.  

Related FAQ: 
What are Team Leagues? What are its benefits in the game?
Where can I see my Team League info and trophy earning?