Run time starts when any element of your HUD appears in the first map.
Ends on the last frame any element of your HUD can be seen during the escape in the final map.
Entering the rescue during the finale of each campaign must fade to a completely black screen to count as completed.
For runs starting on No Mercy, time starts when you enter first-person view.

It is not required to show a timer for a valid submission, unobstructed gameplay is all you need.

For runs that have multiple campaigns, they can be played in any order you'd like, but each campaign must be played in a single, unbroken instance, from its first map to its last.
You cannot change game versions mid-run, you must commit to what you started with.

All addons are banned from use. Video must be recorded as you play (not demo playback) and be uncut for the duration of run time. Game audio must be clear enough to confirm no addons were used.

Console commands protected under "sv_cheats" are banned during the run as well as the following:
z_difficulty
changelevel ---------- December 27th 2016
kick ------------------- April 19th 2015
thirdpersonshoulder - June 2017
jointeam -------------- August 2017
report_entities -------- February 2018

The following console commands are allowed:
map
cl_viewmodelfovsurvivor
cl_glow commands (for highlights)
cl_crosshair commands
cl_interp/ratio, cl_update/cmdrate
cl_showpos

It is highly recommended to capture your mouse cursor for accurate load removal. Alternatively, you can accept a slight time loss by leaving the red "4" loading icon in the upper-right unobstructed instead. It’s also recommended to have the Livesplit autosplitter shown but it isn’t necessary for submission.
The autosplitter is available by right-clicking in Livesplit, clicking “Edit Splits”, and clicking “Activate”.
A tutorial on how to calculate a without loads time manually is available in the "Guides" section.

Milliseconds (ms) are used only as a tiebreaker, please leave it blank in all other instances.

Co-op specific: Video perspective of the first-loading player is required (likely the host). Can be completed with any number of 2, 3 or 4 players. Only players who were present at the start of the run and completed at least one whole campaign can be credited in the record.

See this other thread for a much deeper explanation on these various rules and why we came to the decisions we have: http://www.speedrun.com/l4d2/thread/wlk68