Hoop damage

From SmashWiki, the Super Smash Bros. wiki

Hoop damage is the damage that a character receives when they are out of the camera's boundaries. The damage is applied at a rate of 1% per second. Once a character reaches 150%, however, damage stops. Hoop damage is present in both Melee and Brawl. It was never mentioned on the Smash Bros. DOJO!!, until April 14, 2008. Hoop damage occurs in every mode, except for Training Mode.

In SSBM, the "hoop" was called the Magnifying Glass, as evidenced by the Lost In Space bonus.