The rules are usually pretty clear, so if you are going to warn someone for teamkilling someone at spawn, then shit will spiral out of control. For the one time an admin does see it, there might be 5 times an admin does not see it, and then you are supposed to warn someone first? Everybody is expected to know the server rules, so when in violation of one, that means that you are willingly breaking the rules. Only vaguely known exploits or clearly new players deserve warnings and I think a warning should consist of a kick, with the admin stating the reason for the kick in admin chat beforehand.
Besides, the only reason the admin did not ban in the screen you posted is probably because it might actually have been an accident. If admins are going to warn for intentional teamkills at spawn, now that is some crappy adminning. That said, banning people who are afk is a little silly in my opinion, a kick would suffice. All sorts of things can cause you to have to very quickly stop playing the game, getting banned for that is a little gay. Still, usually joining spec is an option.
