The number of people in the double round robin is 20* 19=380. Many teams are usually knockout:
They can be divided into four groups, and each group has a seed team to be eliminated.
The last four teams will be eliminated. Or the last four teams win the round robin.
Anyway, it's best to start with elimination, otherwise there will be too many games and no passion.
Divided into four groups, each group circulates, with five teams, A, B, C, D and E, namely A-BA-CA-DA-EB-CB-DB-EC-DC-ED-E.
* * * Ten games. If four venues are held at the same time, the first round can be played for 10 days, sorted by the number of wins. If the number of wins is the same, they are sorted by the difference between gains and losses. Take out a winning team and the last four teams will play. It's easy. If you think there are many games, you will be eliminated. Elimination means A-B C-D E- bye. If a and c win, you are A-E B- bye, and you can play a game at last. In this case, lottery is generally used, otherwise it is unfair.