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Strafe-jumping is a form of trickjump used to increase a player's speed in computer games based on the Quake engine and now the Doom 3 engine. The technique is common in Half-Life 2, QuakeWorld, Quake II, Quake III Arena, Quake 4, QuakeLive, CodeRED: Alien Arena, Nexuiz, Xonotic, Cube, Jedi Knight II, Star Wars Jedi Knight: Jedi Academy, Uberstrike, Soldier of Fortune II, Doom 3, War§ow, Call Of Duty, Return to Castle Wolfenstein, Wolfenstein: Enemy Territory and Tremulous. It is widely accepted as being part of the game.
It had started as a bug in the Quake code base, but it was later decided to be kept intact, as it has become a canonical method used by the player base.
Strafe-jumping requires a very specific combination of mouse and keyboard input. The exact technique involved depends on the game itself; however, most games follow a certain pattern of user actions. In several games, there are entire maps devoted to this, much like obstacle courses.
The movements are usually as follows:
- The player presses the forward key, preparing to make the first jump.
- Still keeping the forward key pressed, the player jumps, adding either the move left or the move right key (ergo the strafe in the term, strafe-jumping). The strafe and jump keys must be pressed at the same time.
- To gain maximum speed, the player must now move the mouse smoothly to around a 85 degree (i.e., turn) in the direction of the strafe, while still holding down the two aforementioned keys. This part is called airstrafing, which is responsible for increase in speed during the jump.
- For successive strafejumps, the player immediately jumps again on landing, swapping the direction of strafe as well as mouse motion.
Done correctly, this will dramatically increase the player's velocity with successive jumps. The only way to learn this technique is by practice. Sequential strafejumping is mainly a matter of muscle memory, as the maximum angle of mouse motion increases slightly with consecutive jumps. Another way to increase jump speed in Quake III is a circle-jump where the player gets over 500 units/sec (standard runspeed is 320 units/sec).
To use this technique while getting around narrow curves, one has to release the forward key while turning into the new direction. This keeps the speed, where one normally would have to either stop jumping or run into the wall.
In some games based on the Quake 3 engine, such as Call of Duty and Wolfenstein: Enemy Territory, fractional increases in jump height can be achieved by playing the game at higher frame rates.
Circle jump start 
The circle jump start is the action performed by the player at the start of the strafe jumping, this gives a sudden burst of speed as opposed to gaining speed with regular strafe jumping. This technique is found to have worked best in Quake 3 engine based games.
The movements are as follows:
- The player stands about 90 degrees from the direction he intends to move in.
- The player then holds forward, the left or right strafe key (depending on which direction he or she intends to take), and turn to face 45 degrees the opposite way. (The player will have turned 135 degrees from his or her original position)
- The player now continues into strafe jumping.
Bunny hopping 
Bunny hopping is a term used for different kinds of movement in games. There are two major usages of the term: In any first person shooter with jumping a player who jumps up and down to avoid being shot is sometimes called a bunny hopper. This is a very basic technique that only works against inexperienced opponents.
More advanced techniques known as bunny hopping use game physics to move faster than the base movement speed, combined with air-control (the ability to change movement direction significantly without losing speed while in the air). Techniques that gain speed without the ability to significantly change direction are often called Strafe-jumping. The methods used to achieve bunny hopping varies from game to game.
Bunny hopping is implemented in QuakeWorld, DeFRaG, Grand Theft Auto: San Andreas, Challenge ProMode Arena, OSP (only with cpm physics) mods for Quake III Arena, Team Fortress Classic, Half-Life Mod Natural Selection, Warsow, Enemy Territory Fortress (a mod for Wolfenstein: Enemy Territory), Painkiller, Kingpin: Life of Crime, Dystopia and Nexuiz.
See also 
- Quake III DeFRaG strafe-jump video in CPM physics at Google Videos (Adobe Flash video)
- Strafe Tutorial (Quake III Arena) (archive link)
- Strafe jumping theory (Why and how it works.)
- Circle jumping theory
- A Trickjump related community with much information on the subject, including practical examples and tutorials.
- The largest Call of Duty series strafe jumping site, with examples and tutorials.