You can stream it if not in attendance
E3 attendees could take part in a t-shirt-prized Wii U Smash Bros. tournament, but it looks like Nintendo's letting the 3DS version strut at Comic-Con (July 25), ahead of its October 3 release.
"Starting at noon, there will be a preliminary round in which groups of four competitors battle it out, with the winner advancing. During the finals, players will duke it out one-on-one to determine the top smasher. Tournament slots are limited, and fans will be able to sign up the day of the event on a first-come, first-served basis."
Sign up where the tournament is being held, the "Nintendo Gaming Lounge at the Marriott Marquis & Marina located at 333 W. Harbor Drive"
Those not braving floods of people and hot weather (smart) can watch the tournament streamed on Nintendo's channel.
Nintendo holding Smash Bros. 3DS tournament at San Diego Comic-Con [Nintendo Everything]