Leagues can either be multi-level (any team can join) or a specific level (only a team at that level can join). All teams start at level one, the lowest level. In leveled leagues, teams can either be promoted to the next level (as long as they aren't already at the highest level, which is 5) or demoted to the previous level (as long as they aren't already at the lowest level, which is 1).
In 10-team leagues 2 teams are promoted and 2 teams are demoted. The two teams that get promoted are the Dominance Trophy winner and the Metro Cup winner. If the same team won both of these awards, then the Finalist Trophy winner is promoted. The 9th and 10th placed teams (regular season) get demoted (except in level 4+ leagues where only the 10th place team is demoted).
In 15-team leagues 3 teams are promoted and 3 teams are demoted. The three teams that get promoted are the Dominance Trophy winner, the Metro Cup winner, and the Finalist Trophy winner. If the same team that won the Dominance Trophy also won either the Metro Cup or the Finalist Trophy, the team with the most wins (regular season) that did not win a trophy gets promoted. The 13th, 14th, and 15th placed teams get demoted (except in level 4+ leagues where only the 14th and 15th place teams are demoted).
Promotions and demotions are only given in leveled leagues. Also, teams in level 2 that are 100+ days old cannot be demoted to level 1.
Higher levels have bigger trophies. See trophy case here.
10-Team Leagues versus 15-Team Leagues
In 10-team leagues 8 out of 10 teams make the playoffs and the schedule has a round-robin structure which each team playing the other 9 teams 8 times (4 times at home and 4 times away). In the playoffs the top seeds are matched up against the bottom seeds with the top seeds getting home ice advantage.
In 15-team leagues 8 out of 15 teams make the playoffs and the league is organized into three divisions. The top four teams in the standings are the three division leaders and the wild card (ranked by wins), while all the other teams are placed 4 through 15 based on wins. Division teams play each other 8 times and the rest of the teams 4 times.
Although it's harder to win a trophy in a 15-team league, the trophies in 15-team leagues are slightly bigger than their 10-team league counterparts.
Public Leagues versus Player-Owned Leagues
Public leagues for each level are automatically created by the game; every time a public league becomes full, a new one of the same level is created to replace it. Public leagues are always 10-team leagues and have a best of three playoffs. Public leagues can be joined by anyone.
Public-owned leagues are created by donators and are customizable. Player-owned leagues can have 10 teams or 15 teams. Playoffs can either be a best of 3, best of 5, or best of 7. Creators of player-owned leagues can make the league multi-level (meaning any level can join but there will be no promotions or demotions) or a specific level (being the level of the creator's team). Furthermore, player-owned leagues can have age minimums. Only donators can create player-owned leagues.
How Leagues Affect Rosters
Trading: Once a league becomes full, the teams in that league can now only trade with the other teams in that league.
Waivers: Players on waivers can be claimed by another team in the league, whereas in the off-season players on waivers cannot be claimed. To view the waivers list, go to your league page and click "Waivers."
Injuries: Only when a team is in a full league is that team susceptible to injuries. You will be notified of injuries at 12 AM (server reset time). To view the injuries list, go to your league page and click "Injuries." Equipment managers help to prevent injuries, doctors can reduce injury time, and athletic therapists can reduce hurt time. Click on "My Team" and then "Staff" to hire and/or use these staff members.
Injuries are annoying because they can create gaps in your lineup, so it is important to create the lineup you want at least before you play your home games. Also, don't forget to insert any injured players back into the lineup once they become healthy again.
The last regular season games are played on day 20. Day 21 is a hiatus and day 22 is the start of the playoffs. Non-playoff teams and teams that get eliminated during the playoffs will have to wait for the Metro Cup to be won and the league to officially end before they can join a new league.