How many Switches do I need to compete in Super Smash Bros. Ultimate?
Whether competing on a Solo or Crews team, Super Smash Bros. Ultimate's competitive format is conducted in 1 v 1 style bouts - the difference between Crews and Solo teams is Crews matches will feature 3 separate 1 v 1 bouts (one after another), while Solo matches will be a single player competing in a best-out-of-three match.
Since all Solo matches are held simultaneously, each Solo player will need to be on their own Switch to complete their matches.
For Crews teams, all 3 players on a team can compete using a single Switch; they will not be competing against all 3 opposing members at the same time, which means they can 'pass the controller' from the first contestant to the next, once their last round is concluded.