Some context: one of the most important skills to master in CS is "counter-strafing", aka stopping your current movement at the right timing, to have perfect accuracy when shooting. If you're currently strafing right, you have to lift your finger from D and tap A before being able to shoot accurately.

Recently, some hardware manufacturers included features at the firmware level to make this automatic for you: if you currently have D pressed, and just tap A, the keyboard will stop pressing D for you, even if your finger is still on the key. There were a lot of discussion withing the community, and the professional scene, about whether or not these hardware features should be allowed or not, as they remove a big part of what's needed to actually master movement in the game.

Yesterday, Valve stepped in and decided that they wouldn't allow these features, kicking you from servers if you're detected to use them. At initial release it looks like false positives are possible as many people reported getting kicked without using them, but this should be fixed soon. Another issue people have is that they effectively also banned "jumpthrows", aka binds allowing you to throw nades perfectly everytime, a feature that had been allowed (and even somewhat implemented by Valve themselves) for years.