Hidden rules — Wiki

What the game decides without telling you: kills, hits, grenades, the knife, switching, reloads, sprinting, prone, ladders, vaulting and name tags.

The rules the game never shows, read from its own code for players, weapons and movement. Lines marked (from the code) are read with a little less certainty and still to be seen in game.

Kills and headshots

A kill is a headshot only when the killing hit lands on the head itself: a neck hit never counts, and a knife or grenade kill never counts, even on the head. The kill feed, the scoreboard's headshots and the Headshot medal all use this.
A kill is a wallbang when the killing bullet went through something you can shoot through; never for the knife or a grenade. A wallbang headshot counts as both.
Falling below a map's kill height deals 100 fall damage: it's a fall death.
The One Tap medal needs a headshot kill on a human enemy with the first round of a trigger pull, more than 0.5 s after your previous shot. It's given when you let go of the trigger; with an automatic gun that pull must fire only the one round.

Getting hit

All the pellets of one Trench Gun blast that hit a player arrive as one hit: one hitmarker and one flinch, sized by their total damage.
Every hit plays a hurt sound on the victim that everyone nearby hears, enemies included, and a headshot has a sound of its own: you can hear a headshot land.
Your character calls out when you're hit, and teammates' characters call out when a teammate near them is hit or dies. Only your team hears these.
Dead teammates watching you see your damage indicators and your hitmarkers.

Grenades

The grenade key puts your gun away at once and takes 0.5 s to get the grenade ready. Let go and it leaves your hand 0.33 s later; your gun is back at 0.43 s. Tap the key and it throws as soon as it's ready: 0.83 s after the press at the soonest. You can hold a ready grenade as long as you like, and there's no throw strength.
You can throw while jumping, falling, crouched, prone or sprinting. Starting a throw drops your aim, stops your sprint and cancels a reload.
Once a grenade is ready, any weapon key puts it back: nothing is thrown and you keep it. It can't be cancelled during the 0.5 s, or once thrown.

The knife

V stabs without switching: your gun goes away at once, the stab hits 0.1 s after the press, and your gun is back about 1 s after it (the 0.77 s stab and a quick draw). It cancels your aim, sprint and any reload, and works jumping, crouched or prone.
The knife can attack straight out of a sprint: the 0.3 s wait after sprinting doesn't apply to it.

Switching and picking up

Key 1 goes to your primary, or to your pistol if the primary is already out; 2 goes to the pistol, or back to the primary; 3 toggles the knife and your last weapon. The mouse wheel steps primary, pistol, knife.
Picking up a gun swaps it for the one in your hands (your primary if you hold the knife): your old gun lies where the new one was, with its ammo. Pick up a rifle with your pistol out and you carry two primaries and no pistol.
A dropped gun keeps its magazine and spare rounds, and is ready to fire the moment it's picked up: no reload and no bolt.
Press the key of the gun you're putting away and it comes straight back.
Switching away mid-bolt or mid-pump saves nothing: the whole cycle starts again when the gun comes back. A gun drawn empty starts reloading by itself.
You can't switch, reload, knife or throw on a ladder, during a stab, or with a grenade out.

Reloading

These cancel a reload: switching weapons, starting a sprint (or sprinting forward at all), pulling a grenade and the quick knife. Cancelled before its rounds count, the reload is lost.
On the Trench Gun, Springfield and Kar 98k Sniper every round loaded also chambers one: stop after one shell and you can shoot at once, with no pump or bolt.
Stop sprinting with an empty magazine and the gun starts reloading by itself.

Aiming and sprinting

You can't aim while reloading, drawing or putting a gun away, on a ladder, sprinting on the ground (in the air you can), going prone, with a grenade out or during a stab. With the knife out, the aim key slows you to aiming speed.
Pressing aim stops a sprint at once. If you can't aim yet, the sights come up as soon as you can while you hold the key.
Hold aim and sprint together and the one pressed last wins; with a scoped rifle, aim always wins. (from the code)
A sprint needs your movement keys within 60° of where you face and the trigger released. A grenade, a stab or a ladder stops it starting; reloading doesn't, the sprint cancels the reload.
A sprint ends when you stop pushing forward, aim, fire, reload, crouch, go prone, press a lean key, throw or stab. (from the code)
You only count as sprinting (for the 0.3 s before you can fire, and for aiming) while you're actually moving forward faster than 0.2 m/s: holding sprint while standing still doesn't count.

Crouch and prone

Going prone from standing takes 0.6 s (0.2 s to crouch, then 0.4 s), and getting up takes 0.6 s too. Each step waits for the one before.
You need room behind you to go prone: a wall or a steep slope within 1.5 m behind you stops it. Another player behind you doesn't.
Prone, a wall within 1.45 m beside or behind you stops you crawling or turning that way.
Prone, you can't crawl while holding the trigger.
Prone, you can look only 45° up or down.
Prone, you can look 75° either side of where your body points; past that your body turns with you, at most 60° a second. (from the code)
You can only be prone on the ground: crawl off a ledge and you come up to a crouch. You can crouch in mid-air, but not on a ladder.
Getting up needs room for the taller body where you are: with something above you, you stay down. (from the code)

Ladders

To get on a ladder from below, walk into it looking up (more than 10°) or jump at it: walking in looking level does nothing.
To get on from the top, back over the edge facing the wall, or face away from it looking steeply down. (from the code)
Getting on puts your gun away and cancels a reload. On a ladder you can't aim, sprint, switch, reload, knife or throw.
On a ladder you can turn only 90° either side of facing it.
Look up to climb and down to go down, at up to 3.4 m/s once you look about 18° or more up or down. (from the code)
At the top you're pushed onto the ledge at 1 m/s. (from the code)
Jumping off throws you away from the ladder: looking at it, 3.3 m/s away and 2.5 m/s up.

Vaulting

You can only vault where the map maker placed a vault spot. Anywhere else, no low wall can be vaulted.
You vault ledges between 32 cm and about 2.16 m above your feet, facing them from up to 50 cm away.
A vault takes 0.2 s for a low ledge, rising to 0.8 s for 1.52 m and higher: straight up, then across, through anything in the way.
Vaulting is the jump key: every jump tries a vault first, from the ground or a ladder, never in mid-air or crouched. Your weapon, aim and sprint don't matter, and a jump right after a vault is a full one.

Jumping and other players

You can't stand on another player: you're pushed straight off, so boosting doesn't work.
There's no double jump.

Moving

Your speed depends on direction: forward and forward-diagonal 100%, sideways 80%, backwards 70%, backwards-diagonal 80%. (from the code)

Seeing and name tags

Names never show over enemies in our matches, or over dead players and bots. Settings.ShowPlayerNames 0 hides them all.
A teammate's name shows when their head is within 90° of where you face and nothing blocks the line to it, at any distance, or while your crosshair is on them.
In the buy phase every teammate's tag shows through walls, with their health, main weapon and tokens. (from the code)
The crosshair turns teal only when the first thing it points at, within 100 m, is a teammate: never through a wall.
The game hides the parts of a player that poke through a wall, such as a gun barrel through a door, so they don't give the player away. It doesn't hide players themselves. (from the code)

Your connection

The server corrects your position when it's off by more than 2.24 cm, at most every 0.1 s.
After each correction your movement keys work at 20% for 0.1 s.

Still to test

Read from the code, but not yet seen in game:

Dying from a fall may give the kill to the last player who damaged you, teammates included.
A frag that kills after its thrower has died should show no grenade icon in the kill feed and give no grenade medal.
With the knife out, stabs come at most every 0.9 s, not the 0.7 s its page gives.
Letting go of the trigger may drop an early click a semi-automatic gun had queued.
Looking at a dropped gun of the same kind as yours may take its spare rounds into yours.
Aiming straight after a hard landing may leave you almost unable to move for a moment.
Two players hitting the same target in the same network update may leave the first without a hitmarker.
Prone with a non-scoped gun while crawling, the sights may need a fresh aim press.

The weapons' own timings (early clicks, reloads, bolts and pumps) are on Weapon handling.