How do speedrunners turn a game's glitches into a sport?

Speedrunning is playing a game, or a part of it, with the goal of finishing as fast as possible. At the top level it rewards knowing the game's machinery as much as fast fingers. Runners follow planned routes, and the routes often use sequence breaking and glitches that let sections be skipped or completed more quickly than the designers intended. Developing the best sequence of actions and stages is called routing.

The sport has roots in the designers themselves. Wolfenstein 3D recorded a par time for each level based on John Romero's own best times, and Doom let players record gameplay as small demo files that were much easier to share than videos on the bulletin boards of the time.

Glitches were once frowned upon. Twin Galaxies' early leaderboards did not allow them, but when runners moved to independent leaderboards their use became increasingly common, and many categories now exist, including glitchless runs. It fits a larger pattern called unintentional emergence, where players find uses for a game that its designers never planned. Quake's rocket jumping, Starsiege: Tribes' skiing and Street Fighter II's combos all began as quirks.

The most extreme form is the tool-assisted speedrun, or TAS. It uses emulators and other tools to build a theoretically perfect playthrough, and it works because the game is deterministic: the same inputs always give the same result. Since every move is recorded, a TAS can even manipulate luck, for example to make the ideal Tetris piece drop. When one was posted without explanation in 2003, many viewers thought it was a human feat, and felt cheated when they learned how it was made.