[TnTSCS]

You have to make a basic workflow (in your mind at least) and know what to do when...

Player joins your server - check
Player attempts to auto-join (their jointeam command is "jointeam 0") - check

Now what do you want? You want to move them to spectate and tell them they cannot use auto-assign? You want to move them to a specific team? If you move them to a specific team, are you going to want them to spawn right away or not? Are you going to display them the model HUD?