From Team Fortress Wiki
Fall damage is a type of damage that is only applied when a player falls from a certain height.
Fall damage is taken by a victim when the victim falls for more than a given distance and lands on a flat horizontal surface, and the damage received mostly depends on how far the victim has fallen since the start of the jump. Landing while crouched will therefore increase Fall damage taken, and the player is thus calculated to have travelled further in this space of time. and is accompanied by a distinct bone crunching noise and blood particles being emitted from the legs for a brief time.
However, Fall damage can be cancelled by utilising a Double jump (or a Triple jump with the Atomizer or a Force jump with the Force-A-Nature) close to the floor, equipping the Pretty Boy's Pocket Pistol, being airblasted away from the floor at an angle, or explosive jumping away from the floor with precise timing. The Mantreads can also offset fall damage from the user if they successfully land on an opponent, inflicting 3 times the fall damage that would've been taken by the wearer to the target, and the wearer will take no fall damage.
If a player dies from fall damage—including pitfalls such as the southern face of Upward, which instantly kill any player who lands in them—a distinct kill message will be displayed in the kill feed, and an assist will be awarded to anyone who was attacking the victim at the time of death.
Note: Damage Values are approximate and have been determined by Community testing. Since fall damage relates to velocity, and not height, these values do not always apply. If the player is accelerated downwards by explosions above them, for instance, the Fall damage will be greater.
Originally sourced from this document.
| Fall Classic|
Cause an environmental death or suicide using the Force-A-Nature's knockback.
| He Who Celt It|
Use the Sticky Launcher to kill an enemy player via environmental damage.
| Medical Intervention|
Save a falling teammate from dying on impact.