T-Spin

Some games give scoring rewards for twisting a tetromino into a tight space. When this is done with a T tetromino, it is called a T-spin.

Two basic algorithms, with slight variations, have been used in newer games to detect and reward in-place spins:

• Immobile, used in The New Tetris: A twist is recognised if a tetromino locks in a position where it cannot move left, right, or up. There is only a reward if rows are completed in this way.
• 3-corner T, used in Tetris DS and other SRS based games: A T-spin bonus is awarded if all of the following are true:[1]
1. Tetromino being locked is T.
2. Last successful movement of the tetromino was a rotate, as opposed to sideways movement, downward movement, or falling due to gravity. (Canceling lock delay in games that allow it, such as Tetris DS, does not count as a movement.) The tetromino doesn't even have to end up in a different orientation than it was dropped in; setting up the "well-known twist" below in Tetris Worlds or Tetris DS and pressing both rotate buttons (B–A or A–B) will trigger the T-spin bonus even without any net rotation.
3. Three of the 4 squares diagonally adjacent to the T's center are occupied. (In Tetris DS, the walls and floor surrounding the playfield are considered "occupied", while in Tetris Worlds for GBA, they aren't.

Different games add further restrictions:

• 3-corner T no wall, used in Tetris Worlds: The walls and floor surrounding the playfield are not considered "occupied". This means that if a wall kick places the T tetromino with its flat side against the wall or floor, the T-spin will not be recognized. (Kicks that place the flat side against blocks in the playfield still work.)
• 3-corner T no kick, used in Tetris: New Century, iPod Tetris, Tetris Evolution, and most other official guideline games released after 2006: The final rotation must not involve a wall kick, that is, it recognizes only the "well known twist" below.
• Tetris Zone recognises T-spins that involve a wallkick, but will not recognise any T-spin that results in a triple.

Rewards

Rewards for T-spins first appeared in The New Tetris. The game added a reward for T-spins (and for twists involving other pieces), which would trigger an "avalanche." Henk Rogers implied in his planetgamecube.com interview that it was the mobile game Tetris Battle that inspired the T-Spin's current dominating points and garbage rewards, although T-Spins in a nerfed form found their way into prior guideline games such as Tetris worlds. As of 2008, the Tetris Guideline seems to favor the 3-corner T no kick rulings.

A couple of 3-corner T no kick rulings variations:

Soft drop

Rotate left

Soft drop

Rotate once

Or twice