Straferunning
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In video games, particularly in first-person shooters (FPSs), straferunning (known as speed-strafing among players of GoldenEye and Perfect Dark) is a technique that allows a player to run faster through levels by moving forwards and sideways at the same time. The game combines these actions and the player achieves roughly 40 percent greater speed compared to moving in a single direction. The method used by the game can be demonstrated using vector addition. The original Doom was one of the most notable games to allow straferunning.
A player starts at an arbitrary point and presses a button causing them to travel forwards at, for example, 1 "unit" per second. At the same time, the player presses another button causing them to move to the right at the same speed.
Where bold denotes vectors, and i and j represent perpendicular unit vectors:
Then by Pythagoras' theorem, the length of vector a + b (in other words, the speed at which the player travels) is:
Since 
, the speed when moving in both directions at once is faster than when moving in one direction. Players can therefore make use of this increased speed in order to gain some kind of advantage; in GoldenEye 007 and Perfect Dark it is used to complete levels more quickly than would otherwise be possible.
More recent FPS games eliminate this problem, ensuring that a player travelling diagonally moves at the same speed as one moving in the four standard directions or, in some cases, slower.
A similar boost in speed is achieved in Team Fortress Classic, and in the original Doom by holding down the strafe key (which, despite its name, does not cause the player to strafe but rather to sidestep) while running along a wall. This is called wall strafing or wall hugging.
It is also possible to straferun in the MMORPG EverQuest.
In the Nintendo 64 FPS game Forsaken 64, straferunning is referred to as "double-chording". Since the player can move in three dimensions in Forsaken, it is possible to "triple-chord". An example of this would be angling your ship down and to the right, then accelerating forwards, up and left simultaneously. The computer enemies in Forsaken always double-chord but never triple-chord.
