2.1.1 Gamemode: 9on9, classlimit 1
The Highlander gamemode is played 9on9 with a general classlimit of 1. While classlimit 1 is not forced by the config, teams are expected to follow the classlimit at all times during the game. Switching classes to change spawn room is allowed.
2.1.2 Rosters must have a minimum of 10 and a maximum of 20 players
The roster must consist of a minimum of 10 players to be eligible to sign up to competitions. Teams must also adhere to a maximum of 20 players or will risk losing their right to a participation item.
2.1.3 Minimum of 8 players needed to play a match
If you are not able to field 9 players you can choose to play 8 vs 9. If you are not able to field 8 players, a default win will be given to the opposing team.
That is for the higlander league, i presume that the ladder is the same. although it doesnt specify that it is only arena, i am guessing because of 9 on 9