Infinite throw trap
Donkey Kong's Infinite Throw Trap (or ITT) is a technique in which Donkey Kong grabs the opponent repeatedly without throwing the grabbed opponent. This technique is possible to perform in the original Super Smash Bros and in Super Smash Bros. Brawl on Lucas.
Technical details
After grabbing the opponent, Donkey Kong can choose to deal damage (about 6%) to him/her by either tapping forward, R, or A. This causes Donkey Kong to piggyback the opponent. During this time, Donkey Kong can walk around with or throw the opponent until he/she struggles free via button mashing (if the opponent doesn't button mash, he/she will be latched on indefinitely). Once the opponent struggles free, if Donkey Kong is standing still, he can grab again almost immediately. The opponent has a few frames in which to escape or counter. The pattern repeats as follows: Donkey Kong grabs the opponent, he latches on to it dealing some damage, the opponent struggles free, Donkey Kong grabs again, and so on.
Controversy
The ITT is sometimes banned in competitive play because it leads to stalling.
Once the ITT is started, it is almost impossible to escape. The fact that Donkey Kong has the fourth longest horizontal grab range (behind Samus, Link and Yoshi) and widest vertical grab range (which allows Donkey Kong to grab small jumping opponents) adds to this problem.
But most importantly, many consider the best counter strategy is refusing to escape the grab. If the grabbed character doesn't button mash, he/she will stay latched on until the Donkey Kong throws. Because the damage is inflicted when Donkey Kong grabs, when faced by the ITT, many opponents will refuse to escape, leading to a stalemate in which the Donkey Kong, intending to infinite, waits for the opponent to button mash, and the grabbed character, not wanting to deal with escaping the infinite, waits for the Donkey Kong to throw.
However, it is important to note that the technique is escapable. At high enough damages, the opposition will get knocked down from the release, allow him/her to tech. Even though it doesn't look like it, the release has knockback, but no damage. Formerly, it was often banned, but recent tournaments appear to ignore the tactic altogether. But since most high level Smashers can escape the infinite, it usually doesn't make a difference.
The wall infinites
Many characters in the Hyrule Castle stage in SSB can also do a "infinite" using the two walls of the side of the stage. Examples include Captain Falcon's back air at certain areas, Fox's back air into SHFFLd down air, Donkey Kong's forward or back throw, Mario's forward into SHFFLd down air (at lower percentages), and Pikachu's greenhouse of pain (back throws followed by back air into up smash or down special). Pikachu's was made famous through Isai. With good DI, certain Wall Infinites are harder to do.
