Looks like this is a matter of semantics, honestly.
Intentional teamwounding and teamkilling is only allowed after the round is literally over, and only if the person doesn't care about being TK'd.
As it's rarely enforced, it's difficult to rightfully determine what is and isn't acceptable.
I will say, the teamkill appears to have happened after the round as valor already went out.
The donkey kill was clearly before the round was over, though.
So, since this is unusual and convoluted by nature, and as Cosby's only ban was over two years ago, I'm just going to give him a warning.
Be more careful and wait until the round is literally over.
Donkey_Thrower, the thread seems a little unnecessary.
A few CTRL+M's or a "please stop" would have probably done the trick, and as this sort of thing happens nearly every round, it's strange that your first response would be to post a ban thread.
You're technically in the right, but I'd really suggest in a situation like this that you first take it up with the person you have the issue with.