Valve has worked diligently to improve VAC so it's able to identify and remove cheaters, but trying to get rid of annoying and disruptive players is extremely difficult. However, Valve has given game studios the ability to identify and permanently ban players, including those found to be cheating.
"Playing games should be fun. In order to ensure the best possible online multiplayer experience, Valve allows developers to implement their own systems that detect and permanently ban any disruptive players, such as those using cheats," according to the Steam website.
Game developers must still inform Valve when they spot a disruptive player, but the developer is "solely responsible for the decision" - with Valve enforcing a game ban as needed. Banned players will have to speak directly with the developer if any problems arise, and Valve can remove a developer's ability to enforce their own systems.