then you are incorrect.
Because at first you MUST record a demo about him hacking, because what if he came back afterwards or the other day and said "Why was i banned" and then asked for a proof.
Also, it would be very wise at some cases like what i just mentioned, to record a demo about the person before perma banning him.
And just so you can make sure that they don't suddenly disconnect at any second and lose them because you didn't take their steam id, you can simple type in the console "Stats" or something like that, it will show the nicknames, and steam IDs of every single CONNECTED player in the server, afterwards you can go to
steamid.io and paste the steam id of the person that's hacking, make sure it's the same person, and go to
sourcebans and web-ban them. (That is of course if they suddenly disconnected while you were trying to ban them)