In an interview with Glixel, Shintaro Sato, programming director for Splatoon 2 reveals that
There’s also a new mode in Splatoon 2 called League Battle. This will be a mode that players can play either in groups of two or four, and it will present you with a two-hour period in which your group competes with other groups to see how many points you can earn. Because the results of that League Battle play will be displayed in a ranking at the end of every two-hour period, we can give players goals to strive for, and hope to encourage them to keep competing and pushing.
There is also the option to connect 8 Switches via LAN Play. Another mode will be a spectator mode where someone will be able to record the match and potentially put it up online. There was no details given on what services (such as Youtube or Twitch) this would be available on.