The Basic Rules

Screenshot can be seen in the Screenshots Section.
This is Smash!

What is "Super Smash Bros."?
It's a brawling, battling, action-packed video game that features a varied roster of characters for four-player simultaneous melees!

When you hit an opponent, his or her damage meter builds up.

The number at the bottom is the damage meter.

The more damage that builds up, the farther an opponent flies each time he or she gets hit!

An opponent with higher damage flies farther.

Soon, people are flying around like rockets.
And when you fly off the screen in any direction...

Screenshot can be seen in the Screenshots Section.
You lose a life!

Also, in some modes, each time you KO an opponent, you earn points. As an example, you can fight for a mere two minutes in a competition to see who can shoot their opponents off-screen the most.

If you had to call it something, I'd say it's almost like a sport.