What are the competitive rules in Tetris?

Section 6: Competitive Rules

There is no sanctioning federation. Competitive play is organised by event, and the rules that matter are the ones each event fixes:

Which version: classic NES play and Guideline-era play are effectively different games. Events specify the exact build.
Randomiser: the 7-bag is standard under the Guideline; classic versions use a different, less forgiving randomiser.
Rollover and kill screens: classic-era competition contends with the score counter and level behaviour breaking down at high levels, which is part of the challenge rather than a bug to patch.
Input method: controller and technique restrictions (such as hypertapping or rolling) are set per event.
The Classic Tetris World Championship is the best known event, but it is an independent competition, not a governing body.

There is no sanctioning federation. Competitive play is organised by event, and the rules that matter are the ones each event fixes:

Which version: classic NES play and Guideline-era play are effectively different games. Events specify the exact build.
Randomiser: the 7-bag is standard under the Guideline; classic versions use a different, less forgiving randomiser.
Rollover and kill screens: classic-era competition contends with the score counter and level behaviour breaking down at high levels, which is part of the challenge rather than a bug to patch.
Input method: controller and technique restrictions (such as hypertapping or rolling) are set per event.
The Classic Tetris World Championship is the best known event, but it is an independent competition, not a governing body.