Nintendo might shy away from unofficial events a little too often, and in the wrong way, but they sure can kick off officially sanctioned tournaments.
Once again Smash and Splatoon will return to E3, but this time it'll be based around Splatoon 2, and the newly announced Super Smash Bros. (the latter will have a presumably limited roster until everyone gets revealed). The events (Invitational for the former, World Championship for the latter) will run from June 11-12, which hints that Nintendo's Direct will probably reveal Smash before the actual convention starts on June 12.
If you're interested in qualifying, the official rules are below:
via destructoid https://www.destructoid.com/nintendo-is-bringing-back-competitive-smash-and-splatoon-2-at-e3-this-year-495500.phtml