How many team members can you kill before being kicked and for how long are you banned?
On most ranked servers, you can kill up to 4-5 teammates, then you are kicked (unintentional TK penalty).
You will however be instantly kicked and also possibly banned temporarily from the game if you TK at the beginning of the round, roughly the first 10 seconds (intentional TK penalty).
How long you are banned depends on the server admins. Half an hour is a typical duration I observe (friends of my friend get kicked frequently :P)