Because a certain number of reg leader don't have friends, people are only allowed to play for one regiment. If you switch regiments within the league, that's a 2 week ban. If you join a regiment in the league from one that's not in the league, there is a 1 week ban.
Make sure that you have your rosters in before you play your first match. You cannot play your first match without a roster.
The start date is June 5th.