Six into four, you can use the group cycle (fair) way, then play 15 games, four into two, two games. Plus one final, the total is 18 games (you can also directly decide the first place with more points through the results of the round robin, that is, 15 games).
If there are not so many games, you can also draw lots directly, that is, draw four teams to see which two teams are in the top four. Compare the remaining two teams. This * * * only needs five innings.