Plutonium

The best thing to do is report them and provide proof with video evidence of these players. The main reason video proof is required is because there are many false reports of actual good players being banned. Most casuals forget that this game has been out for more than 10 years, and most veterans know all the spawn points, wallbang spots, pre-fire known locations, etc. Make sure to provide it to the server owner or admins of the server you're playing on.