Nintendo was originally planning to live stream the Splatoon 2 North American Open December 2020 finals later today, but that is no longer the case. Nintendo has said that the event will continue, but the live-stream has been called off due to “unexpected executional challenges.” Obviously that doesn't really give us much insight into what's happening, but fans think they know what's causing the issue.
As you know, Nintendo stepped in to stop a Super Smash Bros. Melee. online tournament hosted by The Big House due to the use of “use of illegally copied versions of the game” and a mod called “Slippi.” Ever since that happened, fans have been quite riled up about the situation. A #FreeMelee campaign kicked off on social media, and it spread to other aspects of Nintendo fandom, including the Splatoon 2 side of things. This resulted in a number of teams lined up for the Splatoon 2 North American Open December 2020 finals going with names that somehow referenced the #FreeMelee movement.
Again, Nintendo just provided a vague statement on the situation, and fans are thinking it's tied to #FreeMelee. That's just speculation for now, but it does seem to jive with recent happenings.