From Team Fortress Wiki
Strafing is moving laterally to the direction you're facing. This is one of the best ways to dodge enemy fire, move unpredictably, and watch multiple directions while moving in a straight line.
There are several notable forms of strafing. Circle strafing is moving continually around an opponent, making you difficult to track. Jittering refers to strafing rapidly over a short distance, making it difficult to judge your position. Finally, air strafing is a form of acceleration that allows you to move laterally in the air.
To circle strafe is to move around your opponent. If they have poor aim, poor mouse sensitivity, or lose track of you, you will have the opportunity to shoot them easily while dodging their fire. The technique is performed with the left and right strafe keys in combination with the mouse. When combined with jumping, it can make oneself quite difficult to hit.
Tap the left and right keys very rapidly, with slight variations in rhythm. This will cause you to jerk side to side, encouraging opponents to fire outside your position as they try to aim ahead. This technique sounds ludicrous in theory, but in practice, you will be more difficult to hit with any hitscan weapon.
Air strafing is the technique of combining the strafe keys and mouse movements to change your direction in mid-air. Its primary use is to reach a destination that is hidden around a corner or barrier, but it also slightly increases the velocity of the player and can be used to dodge aerials and avoid successful juggling.
Players who use any of the default movement keys while in the air will produce a short impulse in that direction. This is what allows players to arrest mid-air motion or move a small amount after being knocked into the air. The acceleration is capped or else the player would accrue airspeed while holding or tapping the movement keys.
To air strafe, a player air accelerates to one side while smoothly turning the mouse in that direction. This change in orientation changes the direction of your attempted air acceleration relative to the actual direction of motion, and the component of air acceleration in that direction becomes less than the acceleration cap. This small difference between the component and the cap allows a small amount of further acceleration to occur, and you move slightly in that direction. Thus, a smooth continuous mouse movement ensures that you're always below the acceleration cap and capable of accelerating to that side. This transforms your path through the air into a smooth curve.
Here are the practical steps:
- You move forward through the air.
- You hold one of the strafe keys and none of the other movement keys.
- You smoothly turn the mouse in the direction of the strafe key.
You will accelerate a little bit and curve through the air in that direction. If at any point you press the forward key, back key, or turn in the opposite direction of your strafe key, you will cap out your acceleration, or stop dead, and end your air strafe. Make sure to release the forward key (default) whilst airstrafing.
- Air strafing is an artifact of the air acceleration system developed for Quake's physics engine. In related games, strafe jumping, bunnyhopping, and wall hopping are all exploits of the same acceleration cap. Source uses a similar physics system.