From Team Fortress Wiki
A variety of advanced movement techniques are utilized in the Team Fortress classic series of games. They are listed below.
The game engine has a feature called "air acceleration" that increases and changes the direction of momentum when a strafe key is held while in the air and the mouse is moved evenly in that direction. At the same time, movement speed is based upon a friction-based system, therefore being midair does not subject players to the same rules as regular movement. The exploitation of these rules allows players to quickly move across open ground using a technique called bunnyhopping.
To bunnyhop, first jump and then strafe to the side, moving the mouse in that direction about 45 degrees while in the air; the moment the character touches the ground, immediately jump again and repeat the process in the opposite direction. Jumping must be performed as early as possible to preserve as much speed as possible.
A patch has limited the speeds that can be obtained while bunnyhopping to about 525 Hammer units per second or about 170% medium movement speed. Once the ground is touched at those speeds, momentum will instantly be reduced to about 50% or about 150 Hammer units a second before picking up again. Players must keep just below this cap to bunnyhop successfully on most maps.
Note that the forward key must not be used while bunnyhopping at the risk of losing all of the momentum and speed that has been gained.
A fairly common technique is to grenade or concussion jump into the max movement speed, and then begin bunnyhopping to keep momentum.
Bunnyhopping was completely patched out in Team Fortress 2, aside from a few remnants "using obscure server settings", although air strafing can still be performed by concussion jumping classes like the Soldier and Demoman.
History of bunnyhopping
Bunnyhopping was first introduced in Team Fortress, then was made popular in Team Fortress Classic once it started catching on. Very few people knew about bunnyhopping in Team Fortress Classic when the game was first released, but it slowly started catching on until it became very popular. At first, in Team Fortress Classic, there was no movement speed increase cap, meaning you could speed your character up to as fast as you could react. Later, Valve added a patch in which movement speed increase was capped to ~170% of the character's running speed.
Wall strafing and Strafe jumping
To perform wall strafing, you must run along a wall, hold forward, and then strafe into the wall. This is useful in tight corridors where there is not enough room to do a full strafe jump.
With strafe jumping, you can increase your speed a little bit while in a jump. Unlike bunnyhopping, which does not use the forward key, if you hold the forward key + strafe key + move the mouse in the same direction as the strafing, you will increase your jump distance and speed for that one jump. Strafe jumping is probably the most common movement technique among players, however, bunnyhopping is the most commonly used technique among veteran players. It increases the player's speed, while also allowing them to fight any enemies they encounter.
Chopping is when a character crouches after running, sliding forward a small distance. By repeatedly crouching with good timing, a player can move faster than the normal running speed. This technique is not commonly used as it is slower than strafe jumping. It can be used to conserve a lot of momentum after a rocket and/or grenade jump.
By propelling yourself forward by any means into a ramp, your character will start ramp sliding provided that you have enough speed. However, at the top of the ramp, your character will appear to hit a "lip" and either stop or fly straight up. In order to get past the "lip", you must crouch just as you reach the top of the ramp in order to keep your momentum.
Sharking is the term used for the technique of skimming the surface of water to preserve movement speed. Holding the jump key while in water and moving forward causes characters to stay on the surface of the water without slowing down as they would while swimming. This is analogous to the use of bunnyhopping to preserve momentum on land, and can be combined with it to skim over water in a similar manner.
This is an especially common technique due to the ease at which it can be used and the extreme speed slowdown while swimming.
Pipebomb jumping can be performed by using the Pipebomb Launcher to lay out a pipebomb and then detonate it while jumping over it (similar in manner to a grenade jump). There is a greater degree of control when attempting a pipebomb jump as the Demoman can choose when to detonate the pipebomb.
Grenade jumping is performed with a Concussion or Frag Grenade. First, throw a grenade on the ground. Second, when it is about to detonate, run over it and jump. The knock back will send you flying through the air at a decent speed. Grenade jumps can be combined with a Soldier's rocket or a Demoman's pipebomb to increase the speed and distance. Once airborne, use air strafing to increase your distance. With good timing, a player can chain multiple grenade jumps in the air by releasing the grenade just as it is about to explode. On some maps, Scouts and Medics can cross the whole map without touching the ground.
You can also do HH (hand-held) grenade jumping. You will always be boosted vertically if you aren't moving forward. If you are moving forward as you jump, you can propel yourself great distances at great speeds.
Grenade jumping can also refer to the use of the Grenade Launcher to conduct a similar jump to the above pipebomb jump. While a jump can be preformed, it is less than optimal and requires precise timing. The jump should be used as a means of escape rather than a means of movement as using the Grenade Launcher will give you a shorter distance and lower height jump compared to pipebomb jumping.
Concussion jumping is the preferable mode of movement considering that it deals no damage to the user and its equal or greater knock back.
Handheld grenade jumping
Handheld grenade jumping (hh jumping) is closely related to the regular grenade jump. Instead of throwing the grenade, keep it held the entire time. Right as it is about to explode, jump. The exact timing will change the outcome of your jump. This allows for a much more flexible jump that can be fine tuned to the player's liking. Many times, however, the grenade ends up boosting one more vertically than it should. This can, however, be used to one's advantage on some occasions.
The Engineer does not have enough health to make full use of grenade jumping or concussion grenades. Dispenser jumping allows the Engineer to reach a larger range of heights. When a Dispenser is destroyed, it will create an explosion proportional to the amount of ammo in it. Stand on the Dispenser, jump, and then detonate the Dispenser to effectively create a weaker grenade jump. This takes some practice as a Dispenser can easily hold enough ammo to kill the Engineer.
Sniper jumping is the use of a Sniper Rifle to propel a teammate through the air. This technique takes advantage of the fact that the Sniper Rifle can hit teammates and the powerful knock back that the Sniper Rifle possesses. Unlike other special movement abilities, the Sniper is unable to benefit from this action himself.
Napalm jumping (or IC/Napalm Jumping, IC/Nap Jump, etc.) involves using a Pyro's Napalm Grenades and Incendiary Cannon to propel a Pyro to great distances or heights. It involves laying out napalm grenades, letting them explode, and rocket jumping with the Incendiary Cannon in the flames at the perfect time to propel the player upward and a little forward. The Napalm Grenade deals a set of damage about every 1 second for 9 seconds. You have to IC jump in between these sets of damage the grenade deals to do the jump properly. You can also IC jump at the moment the Napalm Grenade goes explodes, as it hasn't dealt out a set of damage after the explosion. It is generally a tricky maneuver, and not as practical as using a frag grenade to jump but it gets easier with practice and can be of some use. You can also do the easier HH (hand-held) napalm jump, which is a lot more practical