In Tetris games, the player must rotate the tetrominos, changing their orientation so that they will fit into the well in advantageous positions. Official or quasi-official Tetris games give the player the ability to rotate a tetromino either clockwise or counterclockwise as many times as the player can before it locks, with the exception of some earlier PC games which only allowed the player to rotate in one direction. All seven of the tetrominoes can be rotated, including the O piece (which has only one orientation).
If there is no space for the piece in its new orientation, it does not rotate.
However, many games try to nudge the piece when rotating it against the walls of the playfield or against other blocks.
These nudges are called wall kicks.
Initial rotation system (IRS)
Illustration of IRS
Some games, such as TGM series, allow the player to perform "initial rotation" by holding the rotate button during ARE.
IRS allows the player to place pieces faster because more time can be spent on shifting.
It also improves mobility at high gravity because initial rotation is processed before gravity, and with IRS, the player can place a flatter side of the piece on the stack.
In ARS, when the L piece enters,
it normally gets stuck here
So hold rotate left to put it on top
Now DAS left and rotate right
Ideally, the player should be able to use IRS to prevent block out:
