18 teams are freshmen in how to draw lots in groups.

Divide the 18 team into 6 groups, with 3 teams in each group, and play a single round robin, winning 2 out of 3 games. If the first place in each group is promoted, there will be six teams, plus the second team with better performance (judged by the score, if there is duplication, you can play), so that eight teams will be promoted and then eliminated by lottery.