For sourceruns videos it's done in one of two ways. It's either added in post in a video editor, or using a plugin. I'm not sure which plugin it is, but it's most likely not legal for speedrunning.
https://cdn.discordapp.com/attachments/877143798700986388/877616043386884166/HudLayout_2_1.res
Edit the line that says "Waezone", at line 33, and replace the HudLayout.res in the portal/scripts/ folder. I don't think there's any reason for this to not be valid in runs, but that's up to the mods.
It was recently discovered that it is possible to set your mouse sensitivity to a value so high that the game considers it infinite, leading to several new glitchy techniques being discovered.
The rules have now been amended to ban these new techniques in both Inbounds No SLA Legacy and Glitchless.
